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	$78.26	3.152%	$80.7268	$80.73	$80.75	$80.70
Purchase #2	$28.48	13.834%	$32.4199	$32.42	$32.40	$32.40
Purchase #3	$138.94	4.734%	$145.5174	$145.52	$145.50	$145.50
Purchase #4	$82.81	10.417%	$91.4363	$91.44	$91.45	$91.40
Purchase #5	$228.63	5.805%	$241.902	$241.90	$241.90	$241.90
Purchase #6	$161.57	10.811%	$179.0373	$179.04	$179.05	$179.00
Purchase #7	$52.49	6.244%	$55.7675	$55.77	$55.75	$55.80
7 purchase totals =	$771.18		$826.8072	$826.82	$826.80	$826.70