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 $191.91   7.449%   $206.2054   $206.21   $206.20   $206.20  
  Purchase #2 $230.43   4.872%   $241.6565   $241.66   $241.65   $241.70  
  Purchase #3 $114.56   4.521%   $119.7393   $119.74   $119.75   $119.70  
  Purchase #4 $107.77   6.761%   $115.0563   $115.06   $115.05   $115.10  
  Purchase #5 $175.44   12.507%   $197.3823   $197.38   $197.40   $197.40  
  Purchase #6 $159.25   11.593%   $177.7119   $177.71   $177.70   $177.70  
  Purchase #7 $116.53   9.294%   $127.3603   $127.36   $127.35   $127.40  
  7 purchase totals = $1,095.89       $1,185.1120   $1,185.12   $1,185.10   $1,185.20