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	$236.99	9.801%	$260.2174	$260.22	$260.20	$260.20
Purchase #2	$82.40	11.833%	$92.1504	$92.15	$92.15	$92.20
Purchase #3	$156.84	8.664%	$170.4286	$170.43	$170.45	$170.40
Purchase #4	$38.47	11.210%	$42.7825	$42.78	$42.80	$42.80
Purchase #5	$247.48	8.650%	$268.887	$268.89	$268.90	$268.90
Purchase #6	$200.35	11.260%	$222.9094	$222.91	$222.90	$222.90
Purchase #7	$153.66	7.428%	$165.0739	$165.07	$165.05	$165.10
7 purchase totals =	$1,116.19		$1,222.4492	$1,222.45	$1,222.45	$1,222.50