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	$7.90	4.777%	$8.2774	$8.28	$8.30	$8.30
Purchase #2	$98.71	12.766%	$111.3113	$111.31	$111.30	$111.30
Purchase #3	$31.86	6.167%	$33.8248	$33.82	$33.80	$33.80
Purchase #4	$52.38	5.252%	$55.131	$55.13	$55.15	$55.10
Purchase #5	$121.48	3.398%	$125.6079	$125.61	$125.60	$125.60
Purchase #6	$120.65	8.484%	$130.8859	$130.89	$130.90	$130.90
Purchase #7	$18.50	10.276%	$20.4011	$20.40	$20.40	$20.40
7 purchase totals =	$451.48		$485.4394	$485.44	$485.45	$485.40