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	$168.50	13.421%	$191.1144	$191.11	$191.10	$191.10
Purchase #2	$30.38	13.522%	$34.488	$34.49	$34.50	$34.50
Purchase #3	$134.73	11.138%	$149.7362	$149.74	$149.75	$149.70
Purchase #4	$212.89	5.636%	$224.8885	$224.89	$224.90	$224.90
Purchase #5	$132.76	10.682%	$146.9414	$146.94	$146.95	$146.90
Purchase #6	$131.88	12.114%	$147.8559	$147.86	$147.85	$147.90
Purchase #7	$76.98	8.838%	$83.7835	$83.78	$83.80	$83.80
7 purchase totals =	$888.12		$978.8079	$978.81	$978.85	$978.80