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	$233.46	3.748%	$242.2101	$242.21	$242.20	$242.20
Purchase #2	$41.34	13.285%	$46.832	$46.83	$46.85	$46.80
Purchase #3	$109.75	7.306%	$117.7683	$117.77	$117.75	$117.80
Purchase #4	$100.33	9.545%	$109.9065	$109.91	$109.90	$109.90
Purchase #5	$142.38	10.428%	$157.2274	$157.23	$157.25	$157.20
Purchase #6	$148.86	13.192%	$168.4976	$168.50	$168.50	$168.50
Purchase #7	$92.66	13.649%	$105.3072	$105.31	$105.30	$105.30
7 purchase totals =	$868.78		$947.7491	$947.76	$947.75	$947.70