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	$246.74	9.553%	$270.3111	$270.31	$270.30	$270.30
Purchase #2	$91.79	4.191%	$95.6369	$95.64	$95.65	$95.60
Purchase #3	$112.55	8.441%	$122.0503	$122.05	$122.05	$122.10
Purchase #4	$221.53	5.249%	$233.1581	$233.16	$233.15	$233.20
Purchase #5	$62.56	12.318%	$70.2661	$70.27	$70.25	$70.30
Purchase #6	$93.60	5.672%	$98.909	$98.91	$98.90	$98.90
Purchase #7	$184.55	6.241%	$196.0678	$196.07	$196.05	$196.10
7 purchase totals =	$1,013.32		$1,086.3993	$1,086.41	$1,086.35	$1,086.50