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	$83.85	6.728%	$89.4914	$89.49	$89.50	$89.50
Purchase #2	$134.84	3.120%	$139.047	$139.05	$139.05	$139.00
Purchase #3	$220.77	5.273%	$232.4112	$232.41	$232.40	$232.40
Purchase #4	$203.78	5.208%	$214.3929	$214.39	$214.40	$214.40
Purchase #5	$127.64	11.154%	$141.877	$141.88	$141.90	$141.90
Purchase #6	$92.82	4.445%	$96.9458	$96.95	$96.95	$96.90
Purchase #7	$140.35	11.271%	$156.1688	$156.17	$156.15	$156.20
7 purchase totals =	$1,004.05		$1,070.3341	$1,070.34	$1,070.35	$1,070.30