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 $46.28   3.811%   $48.0437   $48.04   $48.05   $48.00  
  Purchase #2 $239.69   7.823%   $258.4409   $258.44   $258.45   $258.40  
  Purchase #3 $91.79   10.348%   $101.2884   $101.29   $101.30   $101.30  
  Purchase #4 $66.30   4.729%   $69.4353   $69.44   $69.45   $69.40  
  Purchase #5 $77.96   6.708%   $83.1896   $83.19   $83.20   $83.20  
  Purchase #6 $43.56   8.519%   $47.2709   $47.27   $47.25   $47.30  
  Purchase #7 $207.31   4.281%   $216.1849   $216.18   $216.20   $216.20  
  7 purchase totals = $772.89       $823.8537   $823.85   $823.90   $823.80