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 $59.32   4.750%   $62.1377   $62.14   $62.15   $62.10  
  Purchase #2 $211.75   10.474%   $233.9287   $233.93   $233.95   $233.90  
  Purchase #3 $96.55   6.681%   $103.0005   $103.00   $103.00   $103.00  
  Purchase #4 $104.76   9.554%   $114.7688   $114.77   $114.75   $114.80  
  Purchase #5 $229.86   9.480%   $251.6507   $251.65   $251.65   $251.70  
  Purchase #6 $78.89   6.128%   $83.7244   $83.72   $83.70   $83.70  
  Purchase #7 $58.97   11.283%   $65.6236   $65.62   $65.60   $65.60  
  7 purchase totals = $840.10       $914.8344   $914.83   $914.80   $914.80