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	$61.89	9.327%	$67.6625	$67.66	$67.65	$67.70
Purchase #2	$184.84	13.413%	$209.6326	$209.63	$209.65	$209.60
Purchase #3	$89.62	12.687%	$100.9901	$100.99	$101.00	$101.00
Purchase #4	$158.41	8.373%	$171.6737	$171.67	$171.65	$171.70
Purchase #5	$80.50	7.354%	$86.42	$86.42	$86.40	$86.40
Purchase #6	$87.36	9.631%	$95.7736	$95.77	$95.75	$95.80
Purchase #7	$78.51	13.696%	$89.2627	$89.26	$89.25	$89.30
7 purchase totals =	$741.13		$821.4152	$821.40	$821.35	$821.50