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	$107.41	11.179%	$119.4174	$119.42	$119.40	$119.40
Purchase #2	$20.58	7.607%	$22.1455	$22.15	$22.15	$22.10
Purchase #3	$97.78	11.261%	$108.791	$108.79	$108.80	$108.80
Purchase #4	$147.25	11.802%	$164.6284	$164.63	$164.65	$164.60
Purchase #5	$247.87	11.276%	$275.8198	$275.82	$275.80	$275.80
Purchase #6	$130.65	12.780%	$147.3471	$147.35	$147.35	$147.30
Purchase #7	$85.64	5.336%	$90.2098	$90.21	$90.20	$90.20
7 purchase totals =	$837.18		$928.3590	$928.37	$928.35	$928.20