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 $151.98   10.261%   $167.5747   $167.57   $167.55   $167.60  
  Purchase #2 $177.35   9.459%   $194.1255   $194.13   $194.15   $194.10  
  Purchase #3 $86.88   11.689%   $97.0354   $97.04   $97.05   $97.00  
  Purchase #4 $84.52   3.504%   $87.4816   $87.48   $87.50   $87.50  
  Purchase #5 $90.48   11.616%   $100.9902   $100.99   $101.00   $101.00  
  Purchase #6 $8.61   6.739%   $9.1902   $9.19   $9.20   $9.20  
  Purchase #7 $76.46   6.574%   $81.4865   $81.49   $81.50   $81.50  
  7 purchase totals = $676.28       $737.8841   $737.89   $737.95   $737.90