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	$221.92	12.700%	$250.1038	$250.10	$250.10	$250.10
Purchase #2	$152.89	12.329%	$171.7398	$171.74	$171.75	$171.70
Purchase #3	$224.37	13.435%	$254.5141	$254.51	$254.50	$254.50
Purchase #4	$242.95	5.598%	$256.5503	$256.55	$256.55	$256.60
Purchase #5	$48.44	6.171%	$51.4292	$51.43	$51.45	$51.40
Purchase #6	$242.72	12.331%	$272.6498	$272.65	$272.65	$272.60
Purchase #7	$182.74	9.755%	$200.5663	$200.57	$200.55	$200.60
7 purchase totals =	$1,316.03		$1,457.5533	$1,457.55	$1,457.55	$1,457.50