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	$75.45	3.836%	$78.3443	$78.34	$78.35	$78.30
Purchase #2	$148.53	11.667%	$165.859	$165.86	$165.85	$165.90
Purchase #3	$27.42	12.488%	$30.8442	$30.84	$30.85	$30.80
Purchase #4	$21.51	3.559%	$22.2755	$22.28	$22.30	$22.30
Purchase #5	$136.40	5.238%	$143.5446	$143.54	$143.55	$143.50
Purchase #6	$31.95	3.295%	$33.0028	$33.00	$33.00	$33.00
Purchase #7	$120.79	8.795%	$131.4135	$131.41	$131.40	$131.40
7 purchase totals =	$562.05		$605.2839	$605.27	$605.30	$605.20