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	$78.32	13.656%	$89.0154	$89.02	$89.00	$89.00
Purchase #2	$55.43	10.434%	$61.2136	$61.21	$61.20	$61.20
Purchase #3	$135.64	8.865%	$147.6645	$147.66	$147.65	$147.70
Purchase #4	$247.88	4.216%	$258.3306	$258.33	$258.35	$258.30
Purchase #5	$156.65	8.194%	$169.4859	$169.49	$169.50	$169.50
Purchase #6	$189.74	5.199%	$199.6046	$199.60	$199.60	$199.60
Purchase #7	$168.91	13.238%	$191.2703	$191.27	$191.25	$191.30
7 purchase totals =	$1,032.57		$1,116.5849	$1,116.58	$1,116.55	$1,116.60