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	$76.75	5.274%	$80.7978	$80.80	$80.80	$80.80
Purchase #2	$111.32	13.844%	$126.7311	$126.73	$126.75	$126.70
Purchase #3	$214.75	11.213%	$238.8299	$238.83	$238.85	$238.80
Purchase #4	$202.79	10.307%	$223.6916	$223.69	$223.70	$223.70
Purchase #5	$220.64	11.382%	$245.7532	$245.75	$245.75	$245.80
Purchase #6	$77.78	13.826%	$88.5339	$88.53	$88.55	$88.50
Purchase #7	$84.46	5.506%	$89.1104	$89.11	$89.10	$89.10
7 purchase totals =	$988.49		$1,093.4479	$1,093.44	$1,093.50	$1,093.40