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 $240.99   10.207%   $265.5878   $265.59   $265.60   $265.60  
  Purchase #2 $111.75   11.598%   $124.7108   $124.71   $124.70   $124.70  
  Purchase #3 $156.74   13.503%   $177.9046   $177.90   $177.90   $177.90  
  Purchase #4 $36.66   6.670%   $39.1052   $39.11   $39.10   $39.10  
  Purchase #5 $154.62   8.140%   $167.2061   $167.21   $167.20   $167.20  
  Purchase #6 $119.59   5.863%   $126.6016   $126.60   $126.60   $126.60  
  Purchase #7 $101.63   8.630%   $110.4007   $110.40   $110.40   $110.40  
  7 purchase totals = $921.98       $1,011.5168   $1,011.52   $1,011.50   $1,011.50