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 $51.49   13.294%   $58.3351   $58.34   $58.35   $58.30  
  Purchase #2 $158.80   8.443%   $172.2075   $172.21   $172.20   $172.20  
  Purchase #3 $16.82   12.454%   $18.9148   $18.91   $18.90   $18.90  
  Purchase #4 $175.31   6.269%   $186.3002   $186.30   $186.30   $186.30  
  Purchase #5 $205.66   4.316%   $214.5363   $214.54   $214.55   $214.50  
  Purchase #6 $33.95   7.576%   $36.5221   $36.52   $36.50   $36.50  
  Purchase #7 $53.89   6.179%   $57.2199   $57.22   $57.20   $57.20  
  7 purchase totals = $695.92       $744.0359   $744.04   $744.00   $743.90