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 $207.66   9.165%   $226.692   $226.69   $226.70   $226.70  
  Purchase #2 $135.63   13.118%   $153.4219   $153.42   $153.40   $153.40  
  Purchase #3 $61.97   5.196%   $65.19   $65.19   $65.20   $65.20  
  Purchase #4 $57.48   5.110%   $60.4172   $60.42   $60.40   $60.40  
  Purchase #5 $212.37   13.720%   $241.5072   $241.51   $241.50   $241.50  
  Purchase #6 $207.90   8.294%   $225.1432   $225.14   $225.15   $225.10  
  Purchase #7 $26.29   12.313%   $29.5271   $29.53   $29.55   $29.50  
  7 purchase totals = $909.30       $1,001.8986   $1,001.90   $1,001.90   $1,001.80