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 $188.76   10.323%   $208.2457   $208.25   $208.25   $208.20  
  Purchase #2 $240.60   10.134%   $264.9824   $264.98   $265.00   $265.00  
  Purchase #3 $165.56   7.477%   $177.9389   $177.94   $177.95   $177.90  
  Purchase #4 $18.87   5.694%   $19.9445   $19.94   $19.95   $19.90  
  Purchase #5 $20.80   13.306%   $23.5676   $23.57   $23.55   $23.60  
  Purchase #6 $187.63   3.767%   $194.698   $194.70   $194.70   $194.70  
  Purchase #7 $238.60   11.458%   $265.9388   $265.94   $265.95   $265.90  
  7 purchase totals = $1,060.82       $1,155.3159   $1,155.32   $1,155.35   $1,155.20