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	$37.56	3.653%	$38.9321	$38.93	$38.95	$38.90
Purchase #2	$65.25	12.257%	$73.2477	$73.25	$73.25	$73.20
Purchase #3	$113.81	8.560%	$123.5521	$123.55	$123.55	$123.60
Purchase #4	$216.56	12.148%	$242.8677	$242.87	$242.85	$242.90
Purchase #5	$226.49	7.489%	$243.4518	$243.45	$243.45	$243.50
Purchase #6	$27.40	3.836%	$28.4511	$28.45	$28.45	$28.50
Purchase #7	$172.76	6.617%	$184.1915	$184.19	$184.20	$184.20
7 purchase totals =	$859.83		$934.6940	$934.69	$934.70	$934.80