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	$67.96	7.620%	$73.1386	$73.14	$73.15	$73.10
Purchase #2	$191.65	10.333%	$211.4532	$211.45	$211.45	$211.50
Purchase #3	$142.44	3.616%	$147.5906	$147.59	$147.60	$147.60
Purchase #4	$152.41	4.420%	$159.1465	$159.15	$159.15	$159.10
Purchase #5	$31.48	10.472%	$34.7766	$34.78	$34.80	$34.80
Purchase #6	$50.27	10.152%	$55.3734	$55.37	$55.35	$55.40
Purchase #7	$97.57	10.753%	$108.0617	$108.06	$108.05	$108.10
7 purchase totals =	$733.78		$789.5406	$789.54	$789.55	$789.60