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	$157.84	9.819%	$173.3383	$173.34	$173.35	$173.30
Purchase #2	$123.63	6.275%	$131.3878	$131.39	$131.40	$131.40
Purchase #3	$36.54	3.641%	$37.8704	$37.87	$37.85	$37.90
Purchase #4	$61.89	5.411%	$65.2389	$65.24	$65.25	$65.20
Purchase #5	$246.28	9.453%	$269.5608	$269.56	$269.55	$269.60
Purchase #6	$91.54	13.334%	$103.7459	$103.75	$103.75	$103.70
Purchase #7	$161.80	10.690%	$179.0964	$179.10	$179.10	$179.10
7 purchase totals =	$879.52		$960.2385	$960.25	$960.25	$960.20