Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $226.58   8.346%   $245.4904   $245.49   $245.50   $245.50  
  Purchase #2 $223.31   10.213%   $246.1167   $246.12   $246.10   $246.10  
  Purchase #3 $155.51   10.485%   $171.8152   $171.82   $171.80   $171.80  
  Purchase #4 $166.54   12.116%   $186.718   $186.72   $186.70   $186.70  
  Purchase #5 $241.62   10.339%   $266.6011   $266.60   $266.60   $266.60  
  Purchase #6 $222.43   4.716%   $232.9198   $232.92   $232.90   $232.90  
  Purchase #7 $181.55   10.666%   $200.9141   $200.91   $200.90   $200.90  
  7 purchase totals = $1,417.54       $1,550.5753   $1,550.58   $1,550.50   $1,550.50