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	$9.51	13.122%	$10.7579	$10.76	$10.75	$10.80
Purchase #2	$49.55	12.464%	$55.7259	$55.73	$55.75	$55.70
Purchase #3	$87.57	9.765%	$96.1212	$96.12	$96.10	$96.10
Purchase #4	$113.89	4.287%	$118.7725	$118.77	$118.75	$118.80
Purchase #5	$86.55	5.484%	$91.2964	$91.30	$91.30	$91.30
Purchase #6	$198.96	5.289%	$209.483	$209.48	$209.50	$209.50
Purchase #7	$83.57	7.865%	$90.1428	$90.14	$90.15	$90.10
7 purchase totals =	$629.60		$672.2997	$672.30	$672.30	$672.30