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	$199.69	10.778%	$221.2126	$221.21	$221.20	$221.20
Purchase #2	$159.39	6.194%	$169.2626	$169.26	$169.25	$169.30
Purchase #3	$57.36	3.756%	$59.5144	$59.51	$59.50	$59.50
Purchase #4	$7.64	10.595%	$8.4495	$8.45	$8.45	$8.40
Purchase #5	$213.73	13.648%	$242.8999	$242.90	$242.90	$242.90
Purchase #6	$99.59	3.719%	$103.2938	$103.29	$103.30	$103.30
Purchase #7	$40.46	7.489%	$43.49	$43.49	$43.50	$43.50
7 purchase totals =	$777.86		$848.1228	$848.11	$848.10	$848.10