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	$6.48	10.588%	$7.1661	$7.17	$7.15	$7.20
Purchase #2	$34.82	9.201%	$38.0238	$38.02	$38.00	$38.00
Purchase #3	$173.37	8.467%	$188.0492	$188.05	$188.05	$188.00
Purchase #4	$122.78	7.296%	$131.738	$131.74	$131.75	$131.70
Purchase #5	$172.39	8.390%	$186.8535	$186.85	$186.85	$186.90
Purchase #6	$162.55	13.813%	$185.003	$185.00	$185.00	$185.00
Purchase #7	$68.37	4.331%	$71.3311	$71.33	$71.35	$71.30
7 purchase totals =	$740.76		$808.1647	$808.16	$808.15	$808.10