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	$73.51	10.133%	$80.9588	$80.96	$80.95	$81.00
Purchase #2	$162.33	3.418%	$167.8784	$167.88	$167.90	$167.90
Purchase #3	$100.69	10.719%	$111.483	$111.48	$111.50	$111.50
Purchase #4	$85.68	4.267%	$89.336	$89.34	$89.35	$89.30
Purchase #5	$53.46	8.735%	$58.1297	$58.13	$58.15	$58.10
Purchase #6	$134.27	11.231%	$149.3499	$149.35	$149.35	$149.30
Purchase #7	$57.91	10.609%	$64.0537	$64.05	$64.05	$64.10
7 purchase totals =	$667.85		$721.1895	$721.19	$721.25	$721.20