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 $21.84   7.526%   $23.4837   $23.48   $23.50   $23.50  
  Purchase #2 $124.41   11.444%   $138.6475   $138.65   $138.65   $138.60  
  Purchase #3 $202.95   10.239%   $223.7301   $223.73   $223.75   $223.70  
  Purchase #4 $158.72   12.437%   $178.46   $178.46   $178.45   $178.50  
  Purchase #5 $126.73   7.544%   $136.2905   $136.29   $136.30   $136.30  
  Purchase #6 $114.43   4.359%   $119.418   $119.42   $119.40   $119.40  
  Purchase #7 $179.56   13.219%   $203.296   $203.30   $203.30   $203.30  
  7 purchase totals = $928.64       $1,023.3258   $1,023.33   $1,023.35   $1,023.30