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 $23.76   6.335%   $25.2652   $25.27   $25.25   $25.30  
  Purchase #2 $164.28   10.757%   $181.9516   $181.95   $181.95   $182.00  
  Purchase #3 $195.61   3.349%   $202.161   $202.16   $202.15   $202.20  
  Purchase #4 $205.53   12.372%   $230.9582   $230.96   $230.95   $231.00  
  Purchase #5 $163.40   7.426%   $175.5341   $175.53   $175.55   $175.50  
  Purchase #6 $29.58   12.143%   $33.1719   $33.17   $33.15   $33.20  
  Purchase #7 $172.93   7.778%   $186.3805   $186.38   $186.40   $186.40  
  7 purchase totals = $955.09       $1,035.4225   $1,035.42   $1,035.40   $1,035.60