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 $245.64   8.435%   $266.3597   $266.36   $266.35   $266.40  
  Purchase #2 $163.40   11.762%   $182.6191   $182.62   $182.60   $182.60  
  Purchase #3 $20.97   11.284%   $23.3363   $23.34   $23.35   $23.30  
  Purchase #4 $34.57   4.688%   $36.1906   $36.19   $36.20   $36.20  
  Purchase #5 $121.39   4.146%   $126.4228   $126.42   $126.40   $126.40  
  Purchase #6 $139.79   10.618%   $154.6329   $154.63   $154.65   $154.60  
  Purchase #7 $209.80   6.727%   $223.9132   $223.91   $223.90   $223.90  
  7 purchase totals = $935.56       $1,013.4746   $1,013.47   $1,013.45   $1,013.40