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	$33.79	11.477%	$37.6681	$37.67	$37.65	$37.70
Purchase #2	$240.57	13.417%	$272.8473	$272.85	$272.85	$272.80
Purchase #3	$178.68	12.425%	$200.881	$200.88	$200.90	$200.90
Purchase #4	$172.76	3.672%	$179.1037	$179.10	$179.10	$179.10
Purchase #5	$191.74	3.177%	$197.8316	$197.83	$197.85	$197.80
Purchase #6	$47.79	5.107%	$50.2306	$50.23	$50.25	$50.20
Purchase #7	$101.45	10.310%	$111.9095	$111.91	$111.90	$111.90
7 purchase totals =	$966.78		$1,050.4718	$1,050.47	$1,050.50	$1,050.40