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	$84.68	8.249%	$91.6653	$91.67	$91.65	$91.70
Purchase #2	$137.81	4.586%	$144.13	$144.13	$144.15	$144.10
Purchase #3	$205.29	6.587%	$218.8125	$218.81	$218.80	$218.80
Purchase #4	$55.84	12.219%	$62.6631	$62.66	$62.65	$62.70
Purchase #5	$89.40	12.449%	$100.5294	$100.53	$100.55	$100.50
Purchase #6	$39.53	5.474%	$41.6939	$41.69	$41.70	$41.70
Purchase #7	$170.34	5.560%	$179.8109	$179.81	$179.80	$179.80
7 purchase totals =	$782.89		$839.3051	$839.30	$839.30	$839.30