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	$29.28	7.865%	$31.5829	$31.58	$31.60	$31.60
Purchase #2	$83.90	13.541%	$95.2609	$95.26	$95.25	$95.30
Purchase #3	$11.48	6.533%	$12.23	$12.23	$12.25	$12.20
Purchase #4	$72.52	11.573%	$80.9127	$80.91	$80.90	$80.90
Purchase #5	$124.86	11.343%	$139.0229	$139.02	$139.00	$139.00
Purchase #6	$32.62	13.717%	$37.0945	$37.09	$37.10	$37.10
Purchase #7	$203.71	10.535%	$225.1708	$225.17	$225.15	$225.20
7 purchase totals =	$558.37		$621.2747	$621.26	$621.25	$621.30