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 $246.65   6.227%   $262.0089   $262.01   $262.00   $262.00  
  Purchase #2 $111.29   12.624%   $125.3392   $125.34   $125.35   $125.30  
  Purchase #3 $220.60   11.588%   $246.1631   $246.16   $246.15   $246.20  
  Purchase #4 $64.49   13.849%   $73.4212   $73.42   $73.40   $73.40  
  Purchase #5 $216.32   9.192%   $236.2041   $236.20   $236.20   $236.20  
  Purchase #6 $89.54   10.864%   $99.2676   $99.27   $99.25   $99.30  
  Purchase #7 $11.36   13.194%   $12.8588   $12.86   $12.85   $12.90  
  7 purchase totals = $960.25       $1,055.2629   $1,055.26   $1,055.20   $1,055.30