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 $248.58   6.532%   $264.8172   $264.82   $264.80   $264.80  
  Purchase #2 $33.62   7.681%   $36.2024   $36.20   $36.20   $36.20  
  Purchase #3 $28.83   9.612%   $31.6011   $31.60   $31.60   $31.60  
  Purchase #4 $43.63   6.152%   $46.3141   $46.31   $46.30   $46.30  
  Purchase #5 $94.30   4.869%   $98.8915   $98.89   $98.90   $98.90  
  Purchase #6 $238.55   9.737%   $261.7776   $261.78   $261.80   $261.80  
  Purchase #7 $22.70   9.717%   $24.9058   $24.91   $24.90   $24.90  
  7 purchase totals = $710.21       $764.5097   $764.51   $764.50   $764.50