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 $168.77   8.471%   $183.0665   $183.07   $183.05   $183.10  
  Purchase #2 $128.79   8.461%   $139.6869   $139.69   $139.70   $139.70  
  Purchase #3 $142.66   8.465%   $154.7362   $154.74   $154.75   $154.70  
  Purchase #4 $176.53   12.301%   $198.245   $198.25   $198.25   $198.20  
  Purchase #5 $118.69   11.497%   $132.3358   $132.34   $132.35   $132.30  
  Purchase #6 $159.56   7.255%   $171.1361   $171.14   $171.15   $171.10  
  Purchase #7 $239.29   10.146%   $263.5684   $263.57   $263.55   $263.60  
  7 purchase totals = $1,134.29       $1,242.7749   $1,242.80   $1,242.80   $1,242.70