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	$95.98	6.778%	$102.4855	$102.49	$102.50	$102.50
Purchase #2	$155.35	10.521%	$171.6944	$171.69	$171.70	$171.70
Purchase #3	$25.82	9.244%	$28.2068	$28.21	$28.20	$28.20
Purchase #4	$35.40	4.830%	$37.1098	$37.11	$37.10	$37.10
Purchase #5	$245.37	10.150%	$270.2751	$270.28	$270.30	$270.30
Purchase #6	$37.47	8.123%	$40.5137	$40.51	$40.50	$40.50
Purchase #7	$167.59	3.620%	$173.6568	$173.66	$173.65	$173.70
7 purchase totals =	$762.98		$823.9421	$823.95	$823.95	$824.00