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 $64.57   9.354%   $70.6099   $70.61   $70.60   $70.60  
  Purchase #2 $172.73   13.419%   $195.9086   $195.91   $195.90   $195.90  
  Purchase #3 $15.76   5.611%   $16.6443   $16.64   $16.65   $16.60  
  Purchase #4 $174.67   8.411%   $189.3615   $189.36   $189.35   $189.40  
  Purchase #5 $59.56   7.672%   $64.1294   $64.13   $64.15   $64.10  
  Purchase #6 $234.93   10.343%   $259.2288   $259.23   $259.25   $259.20  
  Purchase #7 $144.34   3.775%   $149.7888   $149.79   $149.80   $149.80  
  7 purchase totals = $866.56       $945.6713   $945.67   $945.70   $945.60