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	$73.40	13.597%	$83.3802	$83.38	$83.40	$83.40
Purchase #2	$19.73	3.456%	$20.4119	$20.41	$20.40	$20.40
Purchase #3	$199.64	10.796%	$221.1931	$221.19	$221.20	$221.20
Purchase #4	$37.25	4.155%	$38.7977	$38.80	$38.80	$38.80
Purchase #5	$211.74	13.507%	$240.3397	$240.34	$240.35	$240.30
Purchase #6	$81.31	13.717%	$92.4633	$92.46	$92.45	$92.50
Purchase #7	$151.32	12.623%	$170.4211	$170.42	$170.40	$170.40
7 purchase totals =	$774.39		$867.0070	$867.00	$867.00	$867.00