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	$245.56	4.199%	$255.8711	$255.87	$255.85	$255.90
Purchase #2	$92.72	6.850%	$99.0713	$99.07	$99.05	$99.10
Purchase #3	$243.90	4.560%	$255.0218	$255.02	$255.00	$255.00
Purchase #4	$89.68	12.160%	$100.5851	$100.59	$100.60	$100.60
Purchase #5	$61.93	5.176%	$65.1355	$65.14	$65.15	$65.10
Purchase #6	$124.27	5.384%	$130.9607	$130.96	$130.95	$131.00
Purchase #7	$218.45	9.791%	$239.8384	$239.84	$239.85	$239.80
7 purchase totals =	$1,076.51		$1,146.4839	$1,146.49	$1,146.45	$1,146.50