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	$105.46	4.216%	$109.9062	$109.91	$109.90	$109.90
Purchase #2	$82.34	9.533%	$90.1895	$90.19	$90.20	$90.20
Purchase #3	$211.65	8.429%	$229.49	$229.49	$229.50	$229.50
Purchase #4	$181.83	5.350%	$191.5579	$191.56	$191.55	$191.60
Purchase #5	$174.69	9.244%	$190.8383	$190.84	$190.85	$190.80
Purchase #6	$23.72	4.152%	$24.7049	$24.70	$24.70	$24.70
Purchase #7	$164.81	7.531%	$177.2218	$177.22	$177.20	$177.20
7 purchase totals =	$944.50		$1,013.9086	$1,013.91	$1,013.90	$1,013.90