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 $213.57   12.798%   $240.9027   $240.90   $240.90   $240.90  
  Purchase #2 $200.47   13.545%   $227.6237   $227.62   $227.60   $227.60  
  Purchase #3 $246.48   10.676%   $272.7942   $272.79   $272.80   $272.80  
  Purchase #4 $200.41   9.210%   $218.8678   $218.87   $218.85   $218.90  
  Purchase #5 $101.31   8.817%   $110.2425   $110.24   $110.25   $110.20  
  Purchase #6 $178.64   4.667%   $186.9771   $186.98   $187.00   $187.00  
  Purchase #7 $34.46   8.667%   $37.4466   $37.45   $37.45   $37.40  
  7 purchase totals = $1,175.34       $1,294.8546   $1,294.85   $1,294.85   $1,294.80