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 $168.57   4.227%   $175.6955   $175.70   $175.70   $175.70  
  Purchase #2 $45.41   7.686%   $48.9002   $48.90   $48.90   $48.90  
  Purchase #3 $177.32   4.451%   $185.2125   $185.21   $185.20   $185.20  
  Purchase #4 $61.31   13.273%   $69.4477   $69.45   $69.45   $69.40  
  Purchase #5 $207.74   12.726%   $234.177   $234.18   $234.20   $234.20  
  Purchase #6 $170.66   8.566%   $185.2787   $185.28   $185.30   $185.30  
  Purchase #7 $112.72   3.141%   $116.2605   $116.26   $116.25   $116.30  
  7 purchase totals = $943.73       $1,014.9721   $1,014.98   $1,015.00   $1,015.00