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	$95.78	6.604%	$102.1053	$102.11	$102.10	$102.10
Purchase #2	$85.66	12.496%	$96.3641	$96.36	$96.35	$96.40
Purchase #3	$152.80	12.495%	$171.8924	$171.89	$171.90	$171.90
Purchase #4	$144.92	4.160%	$150.9487	$150.95	$150.95	$150.90
Purchase #5	$122.62	3.708%	$127.1667	$127.17	$127.15	$127.20
Purchase #6	$107.61	7.667%	$115.8605	$115.86	$115.85	$115.90
Purchase #7	$150.51	10.199%	$165.8605	$165.86	$165.85	$165.90
7 purchase totals =	$859.90		$930.1982	$930.20	$930.15	$930.30