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 $204.63   3.331%   $211.4462   $211.45   $211.45   $211.40  
  Purchase #2 $182.35   10.390%   $201.2962   $201.30   $201.30   $201.30  
  Purchase #3 $176.79   9.826%   $194.1614   $194.16   $194.15   $194.20  
  Purchase #4 $184.45   11.690%   $206.0122   $206.01   $206.00   $206.00  
  Purchase #5 $162.26   8.635%   $176.2712   $176.27   $176.25   $176.30  
  Purchase #6 $175.59   10.194%   $193.4896   $193.49   $193.50   $193.50  
  Purchase #7 $76.36   4.422%   $79.7366   $79.74   $79.75   $79.70  
  7 purchase totals = $1,162.43       $1,262.4134   $1,262.42   $1,262.40   $1,262.40