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 $201.92   5.612%   $213.2518   $213.25   $213.25   $213.30  
  Purchase #2 $245.47   4.672%   $256.9384   $256.94   $256.95   $256.90  
  Purchase #3 $159.80   9.168%   $174.4505   $174.45   $174.45   $174.50  
  Purchase #4 $91.89   6.432%   $97.8004   $97.80   $97.80   $97.80  
  Purchase #5 $125.47   6.801%   $134.0032   $134.00   $134.00   $134.00  
  Purchase #6 $235.33   10.174%   $259.2725   $259.27   $259.25   $259.30  
  Purchase #7 $114.79   3.596%   $118.9178   $118.92   $118.90   $118.90  
  7 purchase totals = $1,174.67       $1,254.6346   $1,254.63   $1,254.60   $1,254.70