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 $59.93   6.360%   $63.7415   $63.74   $63.75   $63.70  
  Purchase #2 $154.94   8.377%   $167.9193   $167.92   $167.90   $167.90  
  Purchase #3 $218.76   11.754%   $244.4731   $244.47   $244.45   $244.50  
  Purchase #4 $226.33   8.817%   $246.2855   $246.29   $246.30   $246.30  
  Purchase #5 $107.56   8.459%   $116.6585   $116.66   $116.65   $116.70  
  Purchase #6 $151.42   13.723%   $172.1994   $172.20   $172.20   $172.20  
  Purchase #7 $29.38   3.255%   $30.3363   $30.34   $30.35   $30.30  
  7 purchase totals = $948.32       $1,041.6136   $1,041.62   $1,041.60   $1,041.60