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	$12.59	5.662%	$13.3028	$13.30	$13.30	$13.30
Purchase #2	$79.83	12.203%	$89.5717	$89.57	$89.55	$89.60
Purchase #3	$216.94	9.393%	$237.3172	$237.32	$237.30	$237.30
Purchase #4	$219.50	4.604%	$229.6058	$229.61	$229.60	$229.60
Purchase #5	$5.31	9.850%	$5.833	$5.83	$5.85	$5.80
Purchase #6	$250.88	7.562%	$269.8515	$269.85	$269.85	$269.90
Purchase #7	$201.65	10.605%	$223.035	$223.04	$223.05	$223.00
7 purchase totals =	$986.70		$1,068.5170	$1,068.52	$1,068.50	$1,068.50