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 $12.98   13.681%   $14.7558   $14.76   $14.75   $14.80  
  Purchase #2 $91.54   11.424%   $101.9975   $102.00   $102.00   $102.00  
  Purchase #3 $48.55   6.221%   $51.5703   $51.57   $51.55   $51.60  
  Purchase #4 $242.85   11.491%   $270.7559   $270.76   $270.75   $270.80  
  Purchase #5 $83.51   11.151%   $92.8222   $92.82   $92.80   $92.80  
  Purchase #6 $26.93   12.133%   $30.1974   $30.20   $30.20   $30.20  
  Purchase #7 $225.49   3.747%   $233.9391   $233.94   $233.95   $233.90  
  7 purchase totals = $731.85       $796.0382   $796.05   $796.00   $796.10