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	$184.68	10.799%	$204.6236	$204.62	$204.60	$204.60
Purchase #2	$81.40	7.133%	$87.2063	$87.21	$87.20	$87.20
Purchase #3	$247.73	13.621%	$281.4733	$281.47	$281.45	$281.50
Purchase #4	$121.69	9.276%	$132.978	$132.98	$133.00	$133.00
Purchase #5	$100.31	9.551%	$109.8906	$109.89	$109.90	$109.90
Purchase #6	$141.70	11.533%	$158.0423	$158.04	$158.05	$158.00
Purchase #7	$96.45	3.272%	$99.6058	$99.61	$99.60	$99.60
7 purchase totals =	$973.96		$1,073.8199	$1,073.82	$1,073.80	$1,073.80