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 $225.58   5.832%   $238.7358   $238.74   $238.75   $238.70  
  Purchase #2 $158.40   13.405%   $179.6335   $179.63   $179.65   $179.60  
  Purchase #3 $232.53   11.189%   $258.5478   $258.55   $258.55   $258.50  
  Purchase #4 $86.28   10.772%   $95.5741   $95.57   $95.55   $95.60  
  Purchase #5 $185.72   5.488%   $195.9123   $195.91   $195.90   $195.90  
  Purchase #6 $161.86   9.564%   $177.3403   $177.34   $177.35   $177.30  
  Purchase #7 $186.91   5.304%   $196.8237   $196.82   $196.80   $196.80  
  7 purchase totals = $1,237.28       $1,342.5675   $1,342.56   $1,342.55   $1,342.40