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	$61.34	10.655%	$67.8758	$67.88	$67.90	$67.90
Purchase #2	$241.76	5.322%	$254.6265	$254.63	$254.65	$254.60
Purchase #3	$170.56	6.385%	$181.4503	$181.45	$181.45	$181.50
Purchase #4	$43.68	8.221%	$47.2709	$47.27	$47.25	$47.30
Purchase #5	$139.88	11.532%	$156.011	$156.01	$156.00	$156.00
Purchase #6	$56.51	4.682%	$59.1558	$59.16	$59.15	$59.20
Purchase #7	$82.69	13.475%	$93.8325	$93.83	$93.85	$93.80
7 purchase totals =	$796.42		$860.2228	$860.23	$860.25	$860.30