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	$98.27	12.252%	$110.31	$110.31	$110.30	$110.30
Purchase #2	$130.82	6.656%	$139.5274	$139.53	$139.55	$139.50
Purchase #3	$167.81	4.326%	$175.0695	$175.07	$175.05	$175.10
Purchase #4	$158.28	9.124%	$172.7215	$172.72	$172.70	$172.70
Purchase #5	$29.57	13.804%	$33.6518	$33.65	$33.65	$33.70
Purchase #6	$90.79	9.424%	$99.346	$99.35	$99.35	$99.30
Purchase #7	$89.99	11.493%	$100.3326	$100.33	$100.35	$100.30
7 purchase totals =	$765.53		$830.9588	$830.96	$830.95	$830.90