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 $108.36   9.797%   $118.976   $118.98   $119.00   $119.00  
  Purchase #2 $61.93   5.644%   $65.4253   $65.43   $65.45   $65.40  
  Purchase #3 $106.42   7.552%   $114.4568   $114.46   $114.45   $114.50  
  Purchase #4 $153.97   4.658%   $161.1419   $161.14   $161.15   $161.10  
  Purchase #5 $66.57   13.359%   $75.4631   $75.46   $75.45   $75.50  
  Purchase #6 $218.79   11.677%   $244.3381   $244.34   $244.35   $244.30  
  Purchase #7 $214.31   13.662%   $243.589   $243.59   $243.60   $243.60  
  7 purchase totals = $930.35       $1,023.3902   $1,023.40   $1,023.45   $1,023.40