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	$181.33	4.320%	$189.1635	$189.16	$189.15	$189.20
Purchase #2	$120.69	3.454%	$124.8586	$124.86	$124.85	$124.90
Purchase #3	$98.29	7.209%	$105.3757	$105.38	$105.40	$105.40
Purchase #4	$67.69	5.484%	$71.4021	$71.40	$71.40	$71.40
Purchase #5	$84.56	8.362%	$91.6309	$91.63	$91.65	$91.60
Purchase #6	$75.73	5.784%	$80.1102	$80.11	$80.10	$80.10
Purchase #7	$160.34	13.205%	$181.5129	$181.51	$181.50	$181.50
7 purchase totals =	$788.63		$844.0539	$844.05	$844.05	$844.10