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 $241.97   5.224%   $254.6105   $254.61   $254.60   $254.60  
  Purchase #2 $204.89   4.294%   $213.688   $213.69   $213.70   $213.70  
  Purchase #3 $118.52   6.308%   $125.9962   $126.00   $126.00   $126.00  
  Purchase #4 $10.94   7.202%   $11.7279   $11.73   $11.75   $11.70  
  Purchase #5 $23.71   8.208%   $25.6561   $25.66   $25.65   $25.70  
  Purchase #6 $108.34   3.201%   $111.808   $111.81   $111.80   $111.80  
  Purchase #7 $87.63   8.618%   $95.182   $95.18   $95.20   $95.20  
  7 purchase totals = $796.00       $838.6687   $838.68   $838.70   $838.70