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	$237.34	5.470%	$250.3225	$250.32	$250.30	$250.30
Purchase #2	$196.48	4.439%	$205.2017	$205.20	$205.20	$205.20
Purchase #3	$233.88	9.216%	$255.4344	$255.43	$255.45	$255.40
Purchase #4	$37.36	8.551%	$40.5547	$40.55	$40.55	$40.60
Purchase #5	$178.29	6.644%	$190.1356	$190.14	$190.15	$190.10
Purchase #6	$249.77	8.859%	$271.8971	$271.90	$271.90	$271.90
Purchase #7	$152.74	4.596%	$159.7599	$159.76	$159.75	$159.80
7 purchase totals =	$1,285.86		$1,373.3059	$1,373.30	$1,373.30	$1,373.30