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 $214.81   6.428%   $228.618   $228.62   $228.60   $228.60  
  Purchase #2 $84.81   6.109%   $89.991   $89.99   $90.00   $90.00  
  Purchase #3 $57.96   8.236%   $62.7336   $62.73   $62.75   $62.70  
  Purchase #4 $245.95   11.587%   $274.4482   $274.45   $274.45   $274.40  
  Purchase #5 $211.42   5.368%   $222.769   $222.77   $222.75   $222.80  
  Purchase #6 $93.68   8.707%   $101.8367   $101.84   $101.85   $101.80  
  Purchase #7 $71.89   5.386%   $75.762   $75.76   $75.75   $75.80  
  7 purchase totals = $980.52       $1,056.1585   $1,056.16   $1,056.15   $1,056.10