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	$77.41	5.234%	$81.4616	$81.46	$81.45	$81.50
Purchase #2	$135.90	5.788%	$143.7659	$143.77	$143.75	$143.80
Purchase #3	$99.64	9.407%	$109.0131	$109.01	$109.00	$109.00
Purchase #4	$233.31	6.145%	$247.6469	$247.65	$247.65	$247.60
Purchase #5	$166.66	9.692%	$182.8127	$182.81	$182.80	$182.80
Purchase #6	$125.66	12.788%	$141.7294	$141.73	$141.75	$141.70
Purchase #7	$159.66	9.520%	$174.8596	$174.86	$174.85	$174.90
7 purchase totals =	$998.24		$1,081.2892	$1,081.29	$1,081.25	$1,081.30