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 $71.71   6.139%   $76.1123   $76.11   $76.10   $76.10  
  Purchase #2 $107.76   5.289%   $113.4594   $113.46   $113.45   $113.50  
  Purchase #3 $218.30   9.577%   $239.2066   $239.21   $239.20   $239.20  
  Purchase #4 $169.46   9.124%   $184.9215   $184.92   $184.90   $184.90  
  Purchase #5 $94.31   12.776%   $106.359   $106.36   $106.35   $106.40  
  Purchase #6 $169.51   3.689%   $175.7632   $175.76   $175.75   $175.80  
  Purchase #7 $21.48   3.690%   $22.2726   $22.27   $22.25   $22.30  
  7 purchase totals = $852.53       $918.0946   $918.09   $918.00   $918.20