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 $90.82   5.854%   $96.1366   $96.14   $96.15   $96.10  
  Purchase #2 $46.83   10.236%   $51.6235   $51.62   $51.60   $51.60  
  Purchase #3 $60.99   8.797%   $66.3553   $66.36   $66.35   $66.40  
  Purchase #4 $72.62   11.136%   $80.707   $80.71   $80.70   $80.70  
  Purchase #5 $119.61   13.372%   $135.6042   $135.60   $135.60   $135.60  
  Purchase #6 $138.29   9.851%   $151.9129   $151.91   $151.90   $151.90  
  Purchase #7 $179.68   12.664%   $202.4347   $202.43   $202.45   $202.40  
  7 purchase totals = $708.84       $784.7742   $784.77   $784.75   $784.70