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 $22.66   3.824%   $23.5265   $23.53   $23.55   $23.50  
  Purchase #2 $214.88   12.134%   $240.9535   $240.95   $240.95   $241.00  
  Purchase #3 $13.40   5.503%   $14.1374   $14.14   $14.15   $14.10  
  Purchase #4 $58.27   10.429%   $64.347   $64.35   $64.35   $64.30  
  Purchase #5 $197.66   12.816%   $222.9921   $222.99   $223.00   $223.00  
  Purchase #6 $160.79   4.614%   $168.2089   $168.21   $168.20   $168.20  
  Purchase #7 $188.81   12.237%   $211.9147   $211.91   $211.90   $211.90  
  7 purchase totals = $856.47       $946.0801   $946.08   $946.10   $946.00