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 $205.75   12.398%   $231.2589   $231.26   $231.25   $231.30  
  Purchase #2 $70.93   4.349%   $74.0147   $74.01   $74.00   $74.00  
  Purchase #3 $21.69   9.116%   $23.6673   $23.67   $23.65   $23.70  
  Purchase #4 $240.86   3.384%   $249.0107   $249.01   $249.00   $249.00  
  Purchase #5 $168.31   4.501%   $175.8856   $175.89   $175.90   $175.90  
  Purchase #6 $245.82   9.364%   $268.8386   $268.84   $268.85   $268.80  
  Purchase #7 $48.75   6.806%   $52.0679   $52.07   $52.05   $52.10  
  7 purchase totals = $1,002.11       $1,074.7437   $1,074.75   $1,074.70   $1,074.80