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 $75.65   10.419%   $83.532   $83.53   $83.55   $83.50  
  Purchase #2 $12.26   5.356%   $12.9166   $12.92   $12.90   $12.90  
  Purchase #3 $247.78   4.527%   $258.997   $259.00   $259.00   $259.00  
  Purchase #4 $118.53   5.622%   $125.1938   $125.19   $125.20   $125.20  
  Purchase #5 $189.82   13.233%   $214.9389   $214.94   $214.95   $214.90  
  Purchase #6 $229.67   8.858%   $250.0142   $250.01   $250.00   $250.00  
  Purchase #7 $65.68   4.429%   $68.589   $68.59   $68.60   $68.60  
  7 purchase totals = $939.39       $1,014.1815   $1,014.18   $1,014.20   $1,014.10