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	$36.31	10.706%	$40.1973	$40.20	$40.20	$40.20
Purchase #2	$31.82	6.135%	$33.7722	$33.77	$33.75	$33.80
Purchase #3	$84.29	8.721%	$91.6409	$91.64	$91.65	$91.60
Purchase #4	$119.42	10.479%	$131.934	$131.93	$131.95	$131.90
Purchase #5	$33.83	10.778%	$37.4762	$37.48	$37.50	$37.50
Purchase #6	$191.82	10.343%	$211.6599	$211.66	$211.65	$211.70
Purchase #7	$245.44	13.306%	$278.0982	$278.10	$278.10	$278.10
7 purchase totals =	$742.93		$824.7787	$824.78	$824.80	$824.80