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 $57.26   5.756%   $60.5559   $60.56   $60.55   $60.60  
  Purchase #2 $197.72   9.523%   $216.5489   $216.55   $216.55   $216.50  
  Purchase #3 $137.89   12.143%   $154.634   $154.63   $154.65   $154.60  
  Purchase #4 $221.34   5.203%   $232.8563   $232.86   $232.85   $232.90  
  Purchase #5 $52.32   11.535%   $58.3551   $58.36   $58.35   $58.40  
  Purchase #6 $120.93   4.840%   $126.783   $126.78   $126.80   $126.80  
  Purchase #7 $85.31   4.294%   $88.9732   $88.97   $88.95   $89.00  
  7 purchase totals = $872.77       $938.7064   $938.71   $938.70   $938.80