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 $93.65   7.488%   $100.6625   $100.66   $100.65   $100.70  
  Purchase #2 $226.85   6.297%   $241.1347   $241.13   $241.15   $241.10  
  Purchase #3 $153.52   7.622%   $165.2213   $165.22   $165.20   $165.20  
  Purchase #4 $125.59   7.443%   $134.9377   $134.94   $134.95   $134.90  
  Purchase #5 $47.48   3.544%   $49.1627   $49.16   $49.15   $49.20  
  Purchase #6 $53.87   13.739%   $61.2712   $61.27   $61.25   $61.30  
  Purchase #7 $222.45   9.824%   $244.3035   $244.30   $244.30   $244.30  
  7 purchase totals = $923.41       $996.6936   $996.68   $996.65   $996.70