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	$104.27	13.694%	$118.5487	$118.55	$118.55	$118.50
Purchase #2	$185.31	10.375%	$204.5359	$204.54	$204.55	$204.50
Purchase #3	$238.73	7.662%	$257.0215	$257.02	$257.00	$257.00
Purchase #4	$130.98	6.460%	$139.4413	$139.44	$139.45	$139.40
Purchase #5	$24.34	12.334%	$27.3421	$27.34	$27.35	$27.30
Purchase #6	$40.62	4.279%	$42.3581	$42.36	$42.35	$42.40
Purchase #7	$86.32	3.305%	$89.1729	$89.17	$89.15	$89.20
7 purchase totals =	$810.57		$878.4205	$878.42	$878.40	$878.30