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	$96.27	7.142%	$103.1456	$103.15	$103.15	$103.10
Purchase #2	$41.45	7.392%	$44.514	$44.51	$44.50	$44.50
Purchase #3	$134.27	3.597%	$139.0997	$139.10	$139.10	$139.10
Purchase #4	$79.33	3.566%	$82.1589	$82.16	$82.15	$82.20
Purchase #5	$7.74	11.386%	$8.6213	$8.62	$8.60	$8.60
Purchase #6	$39.84	6.166%	$42.2965	$42.30	$42.30	$42.30
Purchase #7	$156.78	7.540%	$168.6012	$168.60	$168.60	$168.60
7 purchase totals =	$555.68		$588.4372	$588.44	$588.40	$588.40