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	$238.86	12.265%	$268.1562	$268.16	$268.15	$268.20
Purchase #2	$176.26	12.871%	$198.9464	$198.95	$198.95	$198.90
Purchase #3	$87.30	13.516%	$99.0995	$99.10	$99.10	$99.10
Purchase #4	$56.89	4.793%	$59.6167	$59.62	$59.60	$59.60
Purchase #5	$249.51	13.656%	$283.5831	$283.58	$283.60	$283.60
Purchase #6	$114.93	6.780%	$122.7223	$122.72	$122.70	$122.70
Purchase #7	$91.44	8.503%	$99.2151	$99.22	$99.20	$99.20
7 purchase totals =	$1,015.19		$1,131.3393	$1,131.35	$1,131.30	$1,131.30