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	$190.30	10.263%	$209.8305	$209.83	$209.85	$209.80
Purchase #2	$63.96	4.596%	$66.8996	$66.90	$66.90	$66.90
Purchase #3	$63.78	10.541%	$70.503	$70.50	$70.50	$70.50
Purchase #4	$157.47	13.645%	$178.9568	$178.96	$178.95	$179.00
Purchase #5	$46.50	9.305%	$50.8268	$50.83	$50.85	$50.80
Purchase #6	$11.68	6.501%	$12.4393	$12.44	$12.45	$12.40
Purchase #7	$250.73	7.309%	$269.0559	$269.06	$269.05	$269.10
7 purchase totals =	$784.42		$858.5119	$858.52	$858.55	$858.50