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	$142.39	13.657%	$161.8362	$161.84	$161.85	$161.80
Purchase #2	$170.37	5.138%	$179.1236	$179.12	$179.10	$179.10
Purchase #3	$140.91	3.303%	$145.5643	$145.56	$145.55	$145.60
Purchase #4	$172.98	13.836%	$196.9135	$196.91	$196.90	$196.90
Purchase #5	$112.32	9.801%	$123.3285	$123.33	$123.35	$123.30
Purchase #6	$224.74	3.345%	$232.2576	$232.26	$232.25	$232.30
Purchase #7	$131.72	11.745%	$147.1905	$147.19	$147.20	$147.20
7 purchase totals =	$1,095.43		$1,186.2142	$1,186.21	$1,186.20	$1,186.20