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	$18.88	8.738%	$20.5297	$20.53	$20.55	$20.50
Purchase #2	$173.47	13.121%	$196.231	$196.23	$196.25	$196.20
Purchase #3	$62.47	4.169%	$65.0744	$65.07	$65.05	$65.10
Purchase #4	$213.37	7.511%	$229.3962	$229.40	$229.40	$229.40
Purchase #5	$146.66	3.148%	$151.2769	$151.28	$151.30	$151.30
Purchase #6	$170.55	12.158%	$191.2855	$191.29	$191.30	$191.30
Purchase #7	$236.96	11.640%	$264.5421	$264.54	$264.55	$264.50
7 purchase totals =	$1,022.36		$1,118.3358	$1,118.34	$1,118.40	$1,118.30