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 $61.51   3.676%   $63.7711   $63.77   $63.75   $63.80  
  Purchase #2 $246.99   7.629%   $265.8329   $265.83   $265.85   $265.80  
  Purchase #3 $191.61   12.422%   $215.4118   $215.41   $215.40   $215.40  
  Purchase #4 $169.37   4.376%   $176.7816   $176.78   $176.80   $176.80  
  Purchase #5 $90.96   12.184%   $102.0426   $102.04   $102.05   $102.00  
  Purchase #6 $218.64   12.746%   $246.5079   $246.51   $246.50   $246.50  
  Purchase #7 $15.30   13.785%   $17.4091   $17.41   $17.40   $17.40  
  7 purchase totals = $994.38       $1,087.7570   $1,087.75   $1,087.75   $1,087.70