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 $63.69   8.144%   $68.8769   $68.88   $68.90   $68.90  
  Purchase #2 $165.55   10.869%   $183.5436   $183.54   $183.55   $183.50  
  Purchase #3 $121.97   13.715%   $138.6982   $138.70   $138.70   $138.70  
  Purchase #4 $24.69   10.249%   $27.2205   $27.22   $27.20   $27.20  
  Purchase #5 $213.46   10.549%   $235.9779   $235.98   $236.00   $236.00  
  Purchase #6 $55.84   9.763%   $61.2917   $61.29   $61.30   $61.30  
  Purchase #7 $15.25   13.621%   $17.3272   $17.33   $17.35   $17.30  
  7 purchase totals = $660.45       $732.9360   $732.94   $733.00   $732.90