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	$195.55	6.720%	$208.691	$208.69	$208.70	$208.70
Purchase #2	$233.34	13.282%	$264.3322	$264.33	$264.35	$264.30
Purchase #3	$24.45	11.799%	$27.3349	$27.33	$27.35	$27.30
Purchase #4	$159.87	6.651%	$170.503	$170.50	$170.50	$170.50
Purchase #5	$93.81	13.535%	$106.5072	$106.51	$106.50	$106.50
Purchase #6	$98.73	3.714%	$102.3968	$102.40	$102.40	$102.40
Purchase #7	$100.83	10.256%	$111.1711	$111.17	$111.15	$111.20
7 purchase totals =	$906.58		$990.9362	$990.93	$990.95	$990.90