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	$18.51	9.142%	$20.2022	$20.20	$20.20	$20.20
Purchase #2	$119.58	4.712%	$125.2146	$125.21	$125.20	$125.20
Purchase #3	$101.74	7.677%	$109.5506	$109.55	$109.55	$109.60
Purchase #4	$173.54	9.353%	$189.7712	$189.77	$189.75	$189.80
Purchase #5	$138.71	5.380%	$146.1726	$146.17	$146.15	$146.20
Purchase #6	$200.57	4.204%	$209.002	$209.00	$209.00	$209.00
Purchase #7	$65.33	11.558%	$72.8808	$72.88	$72.90	$72.90
7 purchase totals =	$817.98		$872.7940	$872.78	$872.75	$872.90