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 $96.85   13.824%   $110.2385   $110.24   $110.25   $110.20  
  Purchase #2 $83.57   12.827%   $94.2895   $94.29   $94.30   $94.30  
  Purchase #3 $170.41   5.553%   $179.8729   $179.87   $179.85   $179.90  
  Purchase #4 $186.49   4.811%   $195.462   $195.46   $195.45   $195.50  
  Purchase #5 $110.99   9.515%   $121.5507   $121.55   $121.55   $121.60  
  Purchase #6 $162.41   12.623%   $182.911   $182.91   $182.90   $182.90  
  Purchase #7 $77.53   6.747%   $82.7609   $82.76   $82.75   $82.80  
  7 purchase totals = $888.25       $967.0855   $967.08   $967.05   $967.20