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	$240.54	13.733%	$273.5734	$273.57	$273.55	$273.60
Purchase #2	$91.62	6.171%	$97.2739	$97.27	$97.25	$97.30
Purchase #3	$13.76	11.663%	$15.3648	$15.36	$15.35	$15.40
Purchase #4	$79.87	10.351%	$88.1373	$88.14	$88.15	$88.10
Purchase #5	$146.43	12.322%	$164.4731	$164.47	$164.45	$164.50
Purchase #6	$39.34	8.629%	$42.7346	$42.73	$42.75	$42.70
Purchase #7	$146.33	4.497%	$152.9105	$152.91	$152.90	$152.90
7 purchase totals =	$757.89		$834.4676	$834.45	$834.40	$834.50