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	$75.32	7.432%	$80.9178	$80.92	$80.90	$80.90
Purchase #2	$242.58	12.784%	$273.5914	$273.59	$273.60	$273.60
Purchase #3	$21.72	5.494%	$22.9133	$22.91	$22.90	$22.90
Purchase #4	$40.68	4.121%	$42.3564	$42.36	$42.35	$42.40
Purchase #5	$140.88	12.552%	$158.5633	$158.56	$158.55	$158.60
Purchase #6	$55.51	11.536%	$61.9136	$61.91	$61.90	$61.90
Purchase #7	$181.71	8.131%	$196.4848	$196.48	$196.50	$196.50
7 purchase totals =	$758.40		$836.7406	$836.73	$836.70	$836.80