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	$199.93	4.641%	$209.2088	$209.21	$209.20	$209.20
Purchase #2	$108.72	8.454%	$117.9112	$117.91	$117.90	$117.90
Purchase #3	$103.77	6.146%	$110.1477	$110.15	$110.15	$110.10
Purchase #4	$68.30	5.147%	$71.8154	$71.82	$71.80	$71.80
Purchase #5	$28.61	11.204%	$31.8155	$31.82	$31.80	$31.80
Purchase #6	$245.29	8.166%	$265.3204	$265.32	$265.30	$265.30
Purchase #7	$35.95	13.806%	$40.9133	$40.91	$40.90	$40.90
7 purchase totals =	$790.57		$847.1323	$847.14	$847.05	$847.00