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	$204.40	9.479%	$223.7751	$223.78	$223.80	$223.80
Purchase #2	$165.96	3.482%	$171.7387	$171.74	$171.75	$171.70
Purchase #3	$95.82	4.283%	$99.924	$99.92	$99.90	$99.90
Purchase #4	$110.50	5.759%	$116.8637	$116.86	$116.85	$116.90
Purchase #5	$224.89	12.457%	$252.9045	$252.90	$252.90	$252.90
Purchase #6	$25.51	11.782%	$28.5156	$28.52	$28.50	$28.50
Purchase #7	$235.34	3.424%	$243.398	$243.40	$243.40	$243.40
7 purchase totals =	$1,062.42		$1,137.1196	$1,137.12	$1,137.10	$1,137.10