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	$82.85	9.673%	$90.8641	$90.86	$90.85	$90.90
Purchase #2	$63.61	11.866%	$71.158	$71.16	$71.15	$71.20
Purchase #3	$124.78	4.352%	$130.2104	$130.21	$130.20	$130.20
Purchase #4	$222.33	12.714%	$250.597	$250.60	$250.60	$250.60
Purchase #5	$141.33	8.831%	$153.8109	$153.81	$153.80	$153.80
Purchase #6	$97.46	9.629%	$106.8444	$106.84	$106.85	$106.80
Purchase #7	$175.81	11.648%	$196.2883	$196.29	$196.30	$196.30
7 purchase totals =	$908.17		$999.7731	$999.77	$999.75	$999.80