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	$202.42	10.273%	$223.2146	$223.21	$223.20	$223.20
Purchase #2	$147.84	12.824%	$166.799	$166.80	$166.80	$166.80
Purchase #3	$19.94	5.288%	$20.9944	$20.99	$21.00	$21.00
Purchase #4	$38.50	10.718%	$42.6264	$42.63	$42.65	$42.60
Purchase #5	$184.55	6.701%	$196.9167	$196.92	$196.90	$196.90
Purchase #6	$34.26	9.286%	$37.4414	$37.44	$37.45	$37.40
Purchase #7	$113.33	13.735%	$128.8959	$128.90	$128.90	$128.90
7 purchase totals =	$740.84		$816.8884	$816.89	$816.90	$816.80