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	$30.33	7.675%	$32.6578	$32.66	$32.65	$32.70
Purchase #2	$50.28	11.814%	$56.2201	$56.22	$56.20	$56.20
Purchase #3	$187.61	6.306%	$199.4407	$199.44	$199.45	$199.40
Purchase #4	$84.87	5.254%	$89.3291	$89.33	$89.35	$89.30
Purchase #5	$161.89	11.737%	$180.891	$180.89	$180.90	$180.90
Purchase #6	$40.75	10.658%	$45.0931	$45.09	$45.10	$45.10
Purchase #7	$184.58	10.815%	$204.5423	$204.54	$204.55	$204.50
7 purchase totals =	$740.31		$808.1741	$808.17	$808.20	$808.10