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	$225.89	11.484%	$251.8312	$251.83	$251.85	$251.80
Purchase #2	$62.72	9.867%	$68.9086	$68.91	$68.90	$68.90
Purchase #3	$83.69	6.253%	$88.9231	$88.92	$88.90	$88.90
Purchase #4	$132.80	13.258%	$150.4066	$150.41	$150.40	$150.40
Purchase #5	$232.47	4.855%	$243.7564	$243.76	$243.75	$243.80
Purchase #6	$172.74	13.723%	$196.4451	$196.45	$196.45	$196.40
Purchase #7	$190.64	11.456%	$212.4797	$212.48	$212.50	$212.50
7 purchase totals =	$1,100.95		$1,212.7507	$1,212.76	$1,212.75	$1,212.70