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	$30.84	3.634%	$31.9607	$31.96	$31.95	$32.00
Purchase #2	$215.37	10.580%	$238.1561	$238.16	$238.15	$238.20
Purchase #3	$223.72	8.500%	$242.7362	$242.74	$242.75	$242.70
Purchase #4	$167.85	10.715%	$185.8351	$185.84	$185.85	$185.80
Purchase #5	$91.25	10.142%	$100.5046	$100.50	$100.50	$100.50
Purchase #6	$159.73	9.594%	$175.0545	$175.05	$175.05	$175.10
Purchase #7	$88.62	3.623%	$91.8307	$91.83	$91.85	$91.80
7 purchase totals =	$977.38		$1,066.0779	$1,066.08	$1,066.10	$1,066.10