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 $184.38   11.752%   $206.0483   $206.05   $206.05   $206.00  
  Purchase #2 $188.39   9.507%   $206.3002   $206.30   $206.30   $206.30  
  Purchase #3 $240.97   6.595%   $256.862   $256.86   $256.85   $256.90  
  Purchase #4 $106.45   10.594%   $117.7273   $117.73   $117.75   $117.70  
  Purchase #5 $56.52   12.568%   $63.6234   $63.62   $63.60   $63.60  
  Purchase #6 $141.63   10.558%   $156.5833   $156.58   $156.60   $156.60  
  Purchase #7 $224.95   9.334%   $245.9468   $245.95   $245.95   $245.90  
  7 purchase totals = $1,143.29       $1,253.0913   $1,253.09   $1,253.10   $1,253.00