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 $104.84   8.124%   $113.3572   $113.36   $113.35   $113.40  
  Purchase #2 $98.98   10.599%   $109.4709   $109.47   $109.45   $109.50  
  Purchase #3 $23.35   9.134%   $25.4828   $25.48   $25.50   $25.50  
  Purchase #4 $154.43   13.346%   $175.0402   $175.04   $175.05   $175.00  
  Purchase #5 $84.73   8.246%   $91.7168   $91.72   $91.70   $91.70  
  Purchase #6 $16.83   6.780%   $17.9711   $17.97   $17.95   $18.00  
  Purchase #7 $170.99   3.517%   $177.0037   $177.00   $177.00   $177.00  
  7 purchase totals = $654.15       $710.0427   $710.04   $710.00   $710.10