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 $228.50   6.624%   $243.6358   $243.64   $243.65   $243.60  
  Purchase #2 $49.84   12.245%   $55.9429   $55.94   $55.95   $55.90  
  Purchase #3 $147.44   11.478%   $164.3632   $164.36   $164.35   $164.40  
  Purchase #4 $242.37   4.781%   $253.9577   $253.96   $253.95   $254.00  
  Purchase #5 $66.30   10.218%   $73.0745   $73.07   $73.05   $73.10  
  Purchase #6 $250.59   12.208%   $281.182   $281.18   $281.20   $281.20  
  Purchase #7 $82.61   13.448%   $93.7194   $93.72   $93.70   $93.70  
  7 purchase totals = $1,067.65       $1,165.8755   $1,165.87   $1,165.85   $1,165.90