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 $111.56   6.123%   $118.3908   $118.39   $118.40   $118.40  
  Purchase #2 $118.36   9.860%   $130.0303   $130.03   $130.05   $130.00  
  Purchase #3 $148.70   3.107%   $153.3201   $153.32   $153.30   $153.30  
  Purchase #4 $157.56   11.163%   $175.1484   $175.15   $175.15   $175.10  
  Purchase #5 $214.98   6.844%   $229.6932   $229.69   $229.70   $229.70  
  Purchase #6 $126.87   8.209%   $137.2848   $137.28   $137.30   $137.30  
  Purchase #7 $139.91   12.326%   $157.1553   $157.16   $157.15   $157.20  
  7 purchase totals = $1,017.94       $1,101.0229   $1,101.02   $1,101.05   $1,101.00