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	$97.63	3.373%	$100.9231	$100.92	$100.90	$100.90
Purchase #2	$101.38	6.697%	$108.1694	$108.17	$108.15	$108.20
Purchase #3	$142.82	6.736%	$152.4404	$152.44	$152.45	$152.40
Purchase #4	$211.41	6.734%	$225.6463	$225.65	$225.65	$225.60
Purchase #5	$25.34	7.413%	$27.2185	$27.22	$27.20	$27.20
Purchase #6	$102.76	6.585%	$109.5267	$109.53	$109.55	$109.50
Purchase #7	$121.43	5.224%	$127.7735	$127.77	$127.75	$127.80
7 purchase totals =	$802.77		$851.6979	$851.70	$851.65	$851.60