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 $131.26   8.762%   $142.761   $142.76   $142.75   $142.80  
  Purchase #2 $72.82   13.336%   $82.5313   $82.53   $82.55   $82.50  
  Purchase #3 $57.67   4.547%   $60.2923   $60.29   $60.30   $60.30  
  Purchase #4 $99.30   5.462%   $104.7238   $104.72   $104.70   $104.70  
  Purchase #5 $66.94   12.222%   $75.1214   $75.12   $75.10   $75.10  
  Purchase #6 $139.91   6.281%   $148.6977   $148.70   $148.70   $148.70  
  Purchase #7 $129.59   8.500%   $140.6052   $140.61   $140.60   $140.60  
  7 purchase totals = $697.49       $754.7327   $754.73   $754.70   $754.70