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 $73.53   12.515%   $82.7323   $82.73   $82.75   $82.70  
  Purchase #2 $229.63   6.592%   $244.7672   $244.77   $244.75   $244.80  
  Purchase #3 $157.55   12.157%   $176.7034   $176.70   $176.70   $176.70  
  Purchase #4 $156.45   9.442%   $171.222   $171.22   $171.20   $171.20  
  Purchase #5 $208.99   6.121%   $221.7823   $221.78   $221.80   $221.80  
  Purchase #6 $132.35   10.707%   $146.5207   $146.52   $146.50   $146.50  
  Purchase #7 $92.34   5.669%   $97.5748   $97.57   $97.55   $97.60  
  7 purchase totals = $1,050.84       $1,141.3027   $1,141.29   $1,141.25   $1,141.30