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 $65.66   5.216%   $69.0848   $69.08   $69.10   $69.10  
  Purchase #2 $108.95   3.399%   $112.6532   $112.65   $112.65   $112.70  
  Purchase #3 $64.28   11.842%   $71.892   $71.89   $71.90   $71.90  
  Purchase #4 $139.36   6.805%   $148.8434   $148.84   $148.85   $148.80  
  Purchase #5 $75.37   9.329%   $82.4013   $82.40   $82.40   $82.40  
  Purchase #6 $139.55   11.480%   $155.5703   $155.57   $155.55   $155.60  
  Purchase #7 $236.55   13.136%   $267.6232   $267.62   $267.60   $267.60  
  7 purchase totals = $829.72       $908.0682   $908.05   $908.05   $908.10