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 $46.38   11.118%   $51.5365   $51.54   $51.55   $51.50  
  Purchase #2 $216.53   11.677%   $241.8142   $241.81   $241.80   $241.80  
  Purchase #3 $66.25   12.418%   $74.4769   $74.48   $74.50   $74.50  
  Purchase #4 $58.90   9.376%   $64.4225   $64.42   $64.40   $64.40  
  Purchase #5 $101.95   6.781%   $108.8632   $108.86   $108.85   $108.90  
  Purchase #6 $179.62   10.314%   $198.146   $198.15   $198.15   $198.10  
  Purchase #7 $178.75   7.117%   $191.4716   $191.47   $191.45   $191.50  
  7 purchase totals = $848.38       $930.7309   $930.73   $930.70   $930.70