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	$150.89	5.751%	$159.5677	$159.57	$159.55	$159.60
Purchase #2	$53.90	10.714%	$59.6748	$59.67	$59.65	$59.70
Purchase #3	$69.96	3.472%	$72.389	$72.39	$72.40	$72.40
Purchase #4	$202.66	8.456%	$219.7969	$219.80	$219.80	$219.80
Purchase #5	$138.70	4.150%	$144.4561	$144.46	$144.45	$144.50
Purchase #6	$84.95	7.470%	$91.2958	$91.30	$91.30	$91.30
Purchase #7	$58.92	3.613%	$61.0488	$61.05	$61.05	$61.00
7 purchase totals =	$759.98		$808.2291	$808.24	$808.20	$808.30