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	$133.76	13.317%	$151.5728	$151.57	$151.55	$151.60
Purchase #2	$73.33	6.609%	$78.1764	$78.18	$78.20	$78.20
Purchase #3	$211.78	7.664%	$228.0108	$228.01	$228.00	$228.00
Purchase #4	$88.54	11.199%	$98.4556	$98.46	$98.45	$98.50
Purchase #5	$154.41	8.527%	$167.5765	$167.58	$167.60	$167.60
Purchase #6	$166.80	12.847%	$188.2288	$188.23	$188.25	$188.20
Purchase #7	$35.52	11.583%	$39.6343	$39.63	$39.65	$39.60
7 purchase totals =	$864.14		$951.6552	$951.66	$951.70	$951.70