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 $88.38   11.170%   $98.252   $98.25   $98.25   $98.30  
  Purchase #2 $44.37   9.161%   $48.4347   $48.43   $48.45   $48.40  
  Purchase #3 $46.72   10.818%   $51.7742   $51.77   $51.75   $51.80  
  Purchase #4 $83.48   11.481%   $93.0643   $93.06   $93.05   $93.10  
  Purchase #5 $235.76   6.538%   $251.174   $251.17   $251.15   $251.20  
  Purchase #6 $20.72   3.135%   $21.3696   $21.37   $21.35   $21.40  
  Purchase #7 $160.29   6.597%   $170.8643   $170.86   $170.85   $170.90  
  7 purchase totals = $679.72       $734.9331   $734.91   $734.85   $735.10