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	$78.94	13.616%	$89.6885	$89.69	$89.70	$89.70
Purchase #2	$47.52	6.757%	$50.7309	$50.73	$50.75	$50.70
Purchase #3	$186.25	5.640%	$196.7545	$196.75	$196.75	$196.80
Purchase #4	$105.75	3.865%	$109.8372	$109.84	$109.85	$109.80
Purchase #5	$242.33	13.301%	$274.5623	$274.56	$274.55	$274.60
Purchase #6	$167.65	5.184%	$176.341	$176.34	$176.35	$176.30
Purchase #7	$221.35	4.721%	$231.7999	$231.80	$231.80	$231.80
7 purchase totals =	$1,049.79		$1,129.7143	$1,129.71	$1,129.75	$1,129.70