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	$113.32	9.228%	$123.7772	$123.78	$123.80	$123.80
Purchase #2	$231.34	7.274%	$248.1677	$248.17	$248.15	$248.20
Purchase #3	$26.31	10.135%	$28.9765	$28.98	$29.00	$29.00
Purchase #4	$225.27	13.435%	$255.535	$255.54	$255.55	$255.50
Purchase #5	$83.92	6.231%	$89.1491	$89.15	$89.15	$89.10
Purchase #6	$91.52	7.420%	$98.3108	$98.31	$98.30	$98.30
Purchase #7	$154.73	3.289%	$159.8191	$159.82	$159.80	$159.80
7 purchase totals =	$926.41		$1,003.7354	$1,003.75	$1,003.75	$1,003.70