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 $244.47   12.651%   $275.3979   $275.40   $275.40   $275.40  
  Purchase #2 $125.66   12.783%   $141.7231   $141.72   $141.70   $141.70  
  Purchase #3 $51.30   13.839%   $58.3994   $58.40   $58.40   $58.40  
  Purchase #4 $154.45   13.523%   $175.3363   $175.34   $175.35   $175.30  
  Purchase #5 $214.70   10.763%   $237.8082   $237.81   $237.80   $237.80  
  Purchase #6 $54.54   11.287%   $60.6959   $60.70   $60.70   $60.70  
  Purchase #7 $217.57   7.789%   $234.5165   $234.52   $234.50   $234.50  
  7 purchase totals = $1,062.69       $1,183.8773   $1,183.89   $1,183.85   $1,183.80