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 $250.51   10.567%   $276.9814   $276.98   $277.00   $277.00  
  Purchase #2 $134.49   8.692%   $146.1799   $146.18   $146.20   $146.20  
  Purchase #3 $135.98   13.810%   $154.7588   $154.76   $154.75   $154.80  
  Purchase #4 $25.87   8.535%   $28.078   $28.08   $28.10   $28.10  
  Purchase #5 $171.56   8.344%   $185.875   $185.88   $185.90   $185.90  
  Purchase #6 $237.55   9.662%   $260.5021   $260.50   $260.50   $260.50  
  Purchase #7 $93.46   3.633%   $96.8554   $96.86   $96.85   $96.90  
  7 purchase totals = $1,049.42       $1,149.2306   $1,149.24   $1,149.30   $1,149.40