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	$93.32	6.336%	$99.2328	$99.23	$99.25	$99.20
Purchase #2	$78.85	3.781%	$81.8313	$81.83	$81.85	$81.80
Purchase #3	$153.89	6.107%	$163.2881	$163.29	$163.30	$163.30
Purchase #4	$40.98	5.277%	$43.1425	$43.14	$43.15	$43.10
Purchase #5	$102.56	7.541%	$110.294	$110.29	$110.30	$110.30
Purchase #6	$59.36	9.130%	$64.7796	$64.78	$64.80	$64.80
Purchase #7	$18.80	7.604%	$20.2296	$20.23	$20.25	$20.20
7 purchase totals =	$547.76		$582.7979	$582.79	$582.90	$582.70