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 $233.94   12.567%   $263.3392   $263.34   $263.35   $263.30  
  Purchase #2 $206.73   11.610%   $230.7314   $230.73   $230.75   $230.70  
  Purchase #3 $67.56   9.470%   $73.9579   $73.96   $73.95   $74.00  
  Purchase #4 $77.39   8.524%   $83.9867   $83.99   $84.00   $84.00  
  Purchase #5 $50.39   3.395%   $52.1007   $52.10   $52.10   $52.10  
  Purchase #6 $122.91   10.158%   $135.3952   $135.40   $135.40   $135.40  
  Purchase #7 $68.26   7.674%   $73.4983   $73.50   $73.50   $73.50  
  7 purchase totals = $827.18       $913.0094   $913.02   $913.05   $913.00