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	$75.75	3.313%	$78.2596	$78.26	$78.25	$78.30
Purchase #2	$199.98	10.574%	$221.1259	$221.13	$221.15	$221.10
Purchase #3	$38.50	13.131%	$43.5554	$43.56	$43.55	$43.60
Purchase #4	$175.97	12.417%	$197.8202	$197.82	$197.80	$197.80
Purchase #5	$152.39	8.862%	$165.8948	$165.89	$165.90	$165.90
Purchase #6	$30.63	5.853%	$32.4228	$32.42	$32.40	$32.40
Purchase #7	$243.75	6.199%	$258.8601	$258.86	$258.85	$258.90
7 purchase totals =	$916.97		$997.9388	$997.94	$997.90	$998.00