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	$20.28	12.365%	$22.7876	$22.79	$22.80	$22.80
Purchase #2	$90.72	9.598%	$99.4273	$99.43	$99.45	$99.40
Purchase #3	$116.63	10.289%	$128.6301	$128.63	$128.65	$128.60
Purchase #4	$204.50	13.505%	$232.1177	$232.12	$232.10	$232.10
Purchase #5	$187.31	3.514%	$193.8921	$193.89	$193.90	$193.90
Purchase #6	$37.77	13.221%	$42.7636	$42.76	$42.75	$42.80
Purchase #7	$109.73	4.223%	$114.3639	$114.36	$114.35	$114.40
7 purchase totals =	$766.94		$833.9823	$833.98	$834.00	$834.00