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	$71.89	12.810%	$81.0991	$81.10	$81.10	$81.10
Purchase #2	$91.48	4.689%	$95.7695	$95.77	$95.75	$95.80
Purchase #3	$32.26	9.459%	$35.3115	$35.31	$35.30	$35.30
Purchase #4	$51.82	8.187%	$56.0625	$56.06	$56.05	$56.10
Purchase #5	$223.38	12.104%	$250.4179	$250.42	$250.40	$250.40
Purchase #6	$54.62	5.104%	$57.4078	$57.41	$57.40	$57.40
Purchase #7	$158.29	4.405%	$165.2627	$165.26	$165.25	$165.30
7 purchase totals =	$683.74		$741.3310	$741.33	$741.25	$741.40