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 $83.28   13.802%   $94.7743   $94.77   $94.75   $94.80  
  Purchase #2 $209.69   11.698%   $234.2195   $234.22   $234.20   $234.20  
  Purchase #3 $127.61   4.530%   $133.3907   $133.39   $133.40   $133.40  
  Purchase #4 $61.55   6.718%   $65.6849   $65.68   $65.70   $65.70  
  Purchase #5 $182.72   11.522%   $203.773   $203.77   $203.75   $203.80  
  Purchase #6 $11.47   10.212%   $12.6413   $12.64   $12.65   $12.60  
  Purchase #7 $42.55   3.116%   $43.8759   $43.88   $43.90   $43.90  
  7 purchase totals = $718.87       $788.3596   $788.35   $788.35   $788.40