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 $123.68   10.738%   $136.9608   $136.96   $136.95   $137.00  
  Purchase #2 $242.95   11.846%   $271.7299   $271.73   $271.75   $271.70  
  Purchase #3 $157.91   3.713%   $163.7732   $163.77   $163.75   $163.80  
  Purchase #4 $35.51   5.283%   $37.386   $37.39   $37.40   $37.40  
  Purchase #5 $59.49   5.314%   $62.6513   $62.65   $62.65   $62.70  
  Purchase #6 $236.41   4.578%   $247.2328   $247.23   $247.25   $247.20  
  Purchase #7 $179.64   9.442%   $196.6016   $196.60   $196.60   $196.60  
  7 purchase totals = $1,035.59       $1,116.3356   $1,116.33   $1,116.35   $1,116.40