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 $68.42   11.575%   $76.3396   $76.34   $76.35   $76.30  
  Purchase #2 $19.92   6.754%   $21.2654   $21.27   $21.25   $21.30  
  Purchase #3 $77.79   8.770%   $84.6122   $84.61   $84.60   $84.60  
  Purchase #4 $81.84   8.164%   $88.5214   $88.52   $88.50   $88.50  
  Purchase #5 $8.33   13.182%   $9.4281   $9.43   $9.45   $9.40  
  Purchase #6 $214.87   13.263%   $243.3682   $243.37   $243.35   $243.40  
  Purchase #7 $196.26   7.430%   $210.8421   $210.84   $210.85   $210.80  
  7 purchase totals = $667.43       $734.3770   $734.38   $734.35   $734.30