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 $179.29   13.629%   $203.7254   $203.73   $203.75   $203.70  
  Purchase #2 $141.93   10.525%   $156.8681   $156.87   $156.85   $156.90  
  Purchase #3 $46.85   12.474%   $52.6941   $52.69   $52.70   $52.70  
  Purchase #4 $76.27   6.468%   $81.2031   $81.20   $81.20   $81.20  
  Purchase #5 $97.67   5.762%   $103.2977   $103.30   $103.30   $103.30  
  Purchase #6 $49.50   6.232%   $52.5848   $52.58   $52.60   $52.60  
  Purchase #7 $75.61   9.760%   $82.9895   $82.99   $83.00   $83.00  
  7 purchase totals = $667.12       $733.3627   $733.36   $733.40   $733.40