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	$241.98	13.649%	$275.0079	$275.01	$275.00	$275.00
Purchase #2	$128.41	7.129%	$137.5643	$137.56	$137.55	$137.60
Purchase #3	$148.83	7.343%	$159.7586	$159.76	$159.75	$159.80
Purchase #4	$78.72	12.144%	$88.2798	$88.28	$88.30	$88.30
Purchase #5	$93.61	10.502%	$103.4409	$103.44	$103.45	$103.40
Purchase #6	$80.41	3.183%	$82.9695	$82.97	$82.95	$83.00
Purchase #7	$122.37	7.677%	$131.7643	$131.76	$131.75	$131.80
7 purchase totals =	$894.33		$978.7853	$978.78	$978.75	$978.90