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	$112.72	6.461%	$120.0028	$120.00	$120.00	$120.00
Purchase #2	$136.34	3.364%	$140.9265	$140.93	$140.95	$140.90
Purchase #3	$232.84	13.707%	$264.7554	$264.76	$264.75	$264.80
Purchase #4	$196.45	6.604%	$209.4236	$209.42	$209.40	$209.40
Purchase #5	$43.56	12.240%	$48.8917	$48.89	$48.90	$48.90
Purchase #6	$240.72	6.158%	$255.5435	$255.54	$255.55	$255.50
Purchase #7	$166.29	8.546%	$180.5011	$180.50	$180.50	$180.50
7 purchase totals =	$1,128.92		$1,220.0446	$1,220.04	$1,220.05	$1,220.00