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 $45.49   10.297%   $50.1741   $50.17   $50.15   $50.20  
  Purchase #2 $73.41   7.121%   $78.6375   $78.64   $78.65   $78.60  
  Purchase #3 $220.49   10.194%   $242.9668   $242.97   $242.95   $243.00  
  Purchase #4 $41.68   11.180%   $46.3398   $46.34   $46.35   $46.30  
  Purchase #5 $98.25   4.651%   $102.8196   $102.82   $102.80   $102.80  
  Purchase #6 $165.60   8.829%   $180.2208   $180.22   $180.20   $180.20  
  Purchase #7 $232.56   13.853%   $264.7765   $264.78   $264.80   $264.80  
  7 purchase totals = $877.48       $965.9351   $965.94   $965.90   $965.90