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 $245.97   3.512%   $254.6085   $254.61   $254.60   $254.60  
  Purchase #2 $109.87   10.377%   $121.2712   $121.27   $121.25   $121.30  
  Purchase #3 $120.36   6.539%   $128.2303   $128.23   $128.25   $128.20  
  Purchase #4 $86.70   5.669%   $91.615   $91.62   $91.60   $91.60  
  Purchase #5 $75.28   10.267%   $83.009   $83.01   $83.00   $83.00  
  Purchase #6 $152.28   13.375%   $172.6475   $172.65   $172.65   $172.60  
  Purchase #7 $217.44   3.151%   $224.2915   $224.29   $224.30   $224.30  
  7 purchase totals = $1,007.90       $1,075.6730   $1,075.68   $1,075.65   $1,075.60