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 $76.82   8.484%   $83.3374   $83.34   $83.35   $83.30  
  Purchase #2 $34.79   6.328%   $36.9915   $36.99   $37.00   $37.00  
  Purchase #3 $98.45   12.600%   $110.8547   $110.85   $110.85   $110.90  
  Purchase #4 $46.95   3.772%   $48.721   $48.72   $48.70   $48.70  
  Purchase #5 $90.55   6.163%   $96.1306   $96.13   $96.15   $96.10  
  Purchase #6 $230.57   5.202%   $242.5643   $242.56   $242.55   $242.60  
  Purchase #7 $70.94   11.640%   $79.1974   $79.20   $79.20   $79.20  
  7 purchase totals = $649.07       $697.7969   $697.79   $697.80   $697.80