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 $117.30   6.568%   $125.0043   $125.00   $125.00   $125.00  
  Purchase #2 $102.26   11.375%   $113.8921   $113.89   $113.90   $113.90  
  Purchase #3 $58.55   9.633%   $64.1901   $64.19   $64.20   $64.20  
  Purchase #4 $138.68   4.461%   $144.8665   $144.87   $144.85   $144.90  
  Purchase #5 $246.34   5.737%   $260.4725   $260.47   $260.45   $260.50  
  Purchase #6 $60.69   4.139%   $63.202   $63.20   $63.20   $63.20  
  Purchase #7 $72.57   6.632%   $77.3828   $77.38   $77.40   $77.40  
  7 purchase totals = $796.39       $849.0103   $849.00   $849.00   $849.10