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 $216.53   8.215%   $234.3179   $234.32   $234.30   $234.30  
  Purchase #2 $110.80   6.179%   $117.6463   $117.65   $117.65   $117.60  
  Purchase #3 $228.45   3.513%   $236.4754   $236.48   $236.50   $236.50  
  Purchase #4 $205.83   6.594%   $219.4024   $219.40   $219.40   $219.40  
  Purchase #5 $248.96   9.709%   $273.1315   $273.13   $273.15   $273.10  
  Purchase #6 $116.59   4.459%   $121.7887   $121.79   $121.80   $121.80  
  Purchase #7 $202.48   6.180%   $214.9933   $214.99   $215.00   $215.00  
  7 purchase totals = $1,329.64       $1,417.7555   $1,417.76   $1,417.80   $1,417.70