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 $120.78   3.201%   $124.6462   $124.65   $124.65   $124.60  
  Purchase #2 $64.85   12.617%   $73.0321   $73.03   $73.05   $73.00  
  Purchase #3 $59.59   11.140%   $66.2283   $66.23   $66.25   $66.20  
  Purchase #4 $208.85   11.153%   $232.143   $232.14   $232.15   $232.10  
  Purchase #5 $97.79   4.208%   $101.905   $101.91   $101.90   $101.90  
  Purchase #6 $203.68   6.783%   $217.4956   $217.50   $217.50   $217.50  
  Purchase #7 $213.33   6.331%   $226.8359   $226.84   $226.85   $226.80  
  7 purchase totals = $968.87       $1,042.2861   $1,042.30   $1,042.35   $1,042.10