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 $202.56   8.117%   $219.0018   $219.00   $219.00   $219.00  
  Purchase #2 $33.96   6.814%   $36.274   $36.27   $36.25   $36.30  
  Purchase #3 $121.84   6.610%   $129.8936   $129.89   $129.90   $129.90  
  Purchase #4 $152.35   10.219%   $167.9186   $167.92   $167.90   $167.90  
  Purchase #5 $126.25   5.170%   $132.7771   $132.78   $132.80   $132.80  
  Purchase #6 $197.51   4.803%   $206.9964   $207.00   $207.00   $207.00  
  Purchase #7 $68.27   9.341%   $74.6471   $74.65   $74.65   $74.60  
  7 purchase totals = $902.74       $967.5086   $967.51   $967.50   $967.50