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 $203.25   6.561%   $216.5852   $216.59   $216.60   $216.60  
  Purchase #2 $45.43   9.153%   $49.5882   $49.59   $49.60   $49.60  
  Purchase #3 $61.87   4.304%   $64.5329   $64.53   $64.55   $64.50  
  Purchase #4 $202.47   12.259%   $227.2908   $227.29   $227.30   $227.30  
  Purchase #5 $163.48   11.450%   $182.1985   $182.20   $182.20   $182.20  
  Purchase #6 $102.37   5.433%   $107.9318   $107.93   $107.95   $107.90  
  Purchase #7 $206.79   6.746%   $220.7401   $220.74   $220.75   $220.70  
  7 purchase totals = $985.66       $1,068.8675   $1,068.87   $1,068.95   $1,068.80