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	$7.85	13.291%	$8.8933	$8.89	$8.90	$8.90
Purchase #2	$96.82	13.664%	$110.0495	$110.05	$110.05	$110.00
Purchase #3	$13.35	5.277%	$14.0545	$14.05	$14.05	$14.10
Purchase #4	$91.98	9.635%	$100.8423	$100.84	$100.85	$100.80
Purchase #5	$73.33	7.603%	$78.9053	$78.91	$78.90	$78.90
Purchase #6	$31.68	5.215%	$33.3321	$33.33	$33.35	$33.30
Purchase #7	$236.94	5.379%	$249.685	$249.69	$249.70	$249.70
7 purchase totals =	$551.95		$595.7620	$595.76	$595.80	$595.70