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	$30.33	10.832%	$33.6153	$33.62	$33.60	$33.60
Purchase #2	$170.99	11.251%	$190.2281	$190.23	$190.25	$190.20
Purchase #3	$71.67	12.705%	$80.7757	$80.78	$80.80	$80.80
Purchase #4	$33.59	12.353%	$37.7394	$37.74	$37.75	$37.70
Purchase #5	$130.95	12.148%	$146.8578	$146.86	$146.85	$146.90
Purchase #6	$64.71	11.192%	$71.9523	$71.95	$71.95	$72.00
Purchase #7	$233.48	3.735%	$242.2005	$242.20	$242.20	$242.20
7 purchase totals =	$735.72		$803.3691	$803.38	$803.40	$803.40