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 $24.43   5.615%   $25.8017   $25.80   $25.80   $25.80  
  Purchase #2 $223.39   6.364%   $237.6065   $237.61   $237.60   $237.60  
  Purchase #3 $91.51   4.367%   $95.5062   $95.51   $95.50   $95.50  
  Purchase #4 $212.48   3.165%   $219.205   $219.21   $219.20   $219.20  
  Purchase #5 $101.46   13.410%   $115.0658   $115.07   $115.05   $115.10  
  Purchase #6 $5.81   9.525%   $6.3634   $6.36   $6.35   $6.40  
  Purchase #7 $96.77   7.708%   $104.229   $104.23   $104.25   $104.20  
  7 purchase totals = $755.85       $803.7776   $803.79   $803.75   $803.80