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	$55.52	6.731%	$59.2571	$59.26	$59.25	$59.30
Purchase #2	$137.34	10.874%	$152.2744	$152.27	$152.25	$152.30
Purchase #3	$100.38	8.714%	$109.1271	$109.13	$109.15	$109.10
Purchase #4	$73.74	11.620%	$82.3086	$82.31	$82.30	$82.30
Purchase #5	$18.71	5.700%	$19.7765	$19.78	$19.80	$19.80
Purchase #6	$12.63	7.765%	$13.6107	$13.61	$13.60	$13.60
Purchase #7	$206.51	13.273%	$233.9201	$233.92	$233.90	$233.90
7 purchase totals =	$604.83		$670.2745	$670.28	$670.25	$670.30