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	$114.51	7.780%	$123.4189	$123.42	$123.40	$123.40
Purchase #2	$89.26	4.343%	$93.1366	$93.14	$93.15	$93.10
Purchase #3	$84.87	5.116%	$89.2119	$89.21	$89.20	$89.20
Purchase #4	$5.41	5.833%	$5.7256	$5.73	$5.75	$5.70
Purchase #5	$72.31	13.789%	$82.2808	$82.28	$82.30	$82.30
Purchase #6	$113.90	10.669%	$126.052	$126.05	$126.05	$126.10
Purchase #7	$248.39	8.433%	$269.3367	$269.34	$269.35	$269.30
7 purchase totals =	$728.65		$789.1625	$789.17	$789.20	$789.10