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	$165.52	12.485%	$186.1852	$186.19	$186.20	$186.20
Purchase #2	$248.56	11.872%	$278.069	$278.07	$278.05	$278.10
Purchase #3	$221.95	9.761%	$243.6145	$243.61	$243.60	$243.60
Purchase #4	$52.87	12.810%	$59.6426	$59.64	$59.65	$59.60
Purchase #5	$120.57	11.609%	$134.567	$134.57	$134.55	$134.60
Purchase #6	$143.96	4.361%	$150.2381	$150.24	$150.25	$150.20
Purchase #7	$6.93	9.191%	$7.5669	$7.57	$7.55	$7.60
7 purchase totals =	$960.36		$1,059.8833	$1,059.89	$1,059.85	$1,059.90