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 $107.34   8.498%   $116.4618   $116.46   $116.45   $116.50  
  Purchase #2 $209.51   8.239%   $226.7715   $226.77   $226.75   $226.80  
  Purchase #3 $116.34   4.557%   $121.6416   $121.64   $121.65   $121.60  
  Purchase #4 $166.29   3.597%   $172.2715   $172.27   $172.25   $172.30  
  Purchase #5 $163.47   4.525%   $170.867   $170.87   $170.85   $170.90  
  Purchase #6 $219.56   5.189%   $230.953   $230.95   $230.95   $231.00  
  Purchase #7 $225.32   5.290%   $237.2394   $237.24   $237.25   $237.20  
  7 purchase totals = $1,207.83       $1,276.2058   $1,276.20   $1,276.15   $1,276.30