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 $248.63   8.842%   $270.6139   $270.61   $270.60   $270.60  
  Purchase #2 $138.48   4.601%   $144.8515   $144.85   $144.85   $144.90  
  Purchase #3 $41.32   8.256%   $44.7314   $44.73   $44.75   $44.70  
  Purchase #4 $187.68   4.216%   $195.5926   $195.59   $195.60   $195.60  
  Purchase #5 $141.26   10.614%   $156.2533   $156.25   $156.25   $156.30  
  Purchase #6 $24.39   11.623%   $27.2248   $27.22   $27.20   $27.20  
  Purchase #7 $174.58   11.430%   $194.5345   $194.53   $194.55   $194.50  
  7 purchase totals = $956.34       $1,033.8020   $1,033.78   $1,033.80   $1,033.80