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	$248.73	11.151%	$276.4659	$276.47	$276.45	$276.50
Purchase #2	$74.30	8.809%	$80.8451	$80.85	$80.85	$80.80
Purchase #3	$191.61	13.717%	$217.8931	$217.89	$217.90	$217.90
Purchase #4	$236.63	12.732%	$266.7577	$266.76	$266.75	$266.80
Purchase #5	$149.61	11.179%	$166.3349	$166.33	$166.35	$166.30
Purchase #6	$35.54	10.423%	$39.2443	$39.24	$39.25	$39.20
Purchase #7	$222.59	7.114%	$238.4251	$238.43	$238.45	$238.40
7 purchase totals =	$1,159.01		$1,285.9661	$1,285.97	$1,286.00	$1,285.90