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 $86.57   9.261%   $94.5872   $94.59   $94.60   $94.60  
  Purchase #2 $161.48   13.738%   $183.6641   $183.66   $183.65   $183.70  
  Purchase #3 $138.95   4.467%   $145.1569   $145.16   $145.15   $145.20  
  Purchase #4 $186.45   4.227%   $194.3312   $194.33   $194.35   $194.30  
  Purchase #5 $77.50   4.548%   $81.0247   $81.02   $81.00   $81.00  
  Purchase #6 $46.41   9.797%   $50.9568   $50.96   $50.95   $51.00  
  Purchase #7 $163.87   3.561%   $169.7054   $169.71   $169.70   $169.70  
  7 purchase totals = $861.23       $919.4263   $919.43   $919.40   $919.50