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 $45.95   5.647%   $48.5448   $48.54   $48.55   $48.50  
  Purchase #2 $145.96   8.834%   $158.8541   $158.85   $158.85   $158.90  
  Purchase #3 $56.68   11.852%   $63.3977   $63.40   $63.40   $63.40  
  Purchase #4 $195.40   4.838%   $204.8535   $204.85   $204.85   $204.90  
  Purchase #5 $135.78   13.678%   $154.352   $154.35   $154.35   $154.40  
  Purchase #6 $20.83   3.414%   $21.5411   $21.54   $21.55   $21.50  
  Purchase #7 $127.52   4.639%   $133.4357   $133.44   $133.45   $133.40  
  7 purchase totals = $728.12       $784.9789   $784.97   $785.00   $785.00