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 $23.36   10.393%   $25.7878   $25.79   $25.80   $25.80  
  Purchase #2 $179.94   12.239%   $201.9629   $201.96   $201.95   $202.00  
  Purchase #3 $195.63   6.173%   $207.7062   $207.71   $207.70   $207.70  
  Purchase #4 $69.35   9.535%   $75.9625   $75.96   $75.95   $76.00  
  Purchase #5 $92.88   6.720%   $99.1215   $99.12   $99.10   $99.10  
  Purchase #6 $234.70   7.266%   $251.7533   $251.75   $251.75   $251.80  
  Purchase #7 $191.80   4.379%   $200.1989   $200.20   $200.20   $200.20  
  7 purchase totals = $987.66       $1,062.4931   $1,062.49   $1,062.45   $1,062.60