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 $187.82   4.314%   $195.9226   $195.92   $195.90   $195.90  
  Purchase #2 $210.71   3.445%   $217.969   $217.97   $217.95   $218.00  
  Purchase #3 $20.66   11.115%   $22.9564   $22.96   $22.95   $23.00  
  Purchase #4 $216.68   4.388%   $226.1879   $226.19   $226.20   $226.20  
  Purchase #5 $35.75   13.366%   $40.5283   $40.53   $40.55   $40.50  
  Purchase #6 $204.91   6.375%   $217.973   $217.97   $217.95   $218.00  
  Purchase #7 $41.82   3.196%   $43.1566   $43.16   $43.15   $43.20  
  7 purchase totals = $918.35       $964.6938   $964.70   $964.65   $964.80