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	$139.62	7.871%	$150.6095	$150.61	$150.60	$150.60
Purchase #2	$77.74	11.295%	$86.5207	$86.52	$86.50	$86.50
Purchase #3	$101.99	12.297%	$114.5317	$114.53	$114.55	$114.50
Purchase #4	$227.97	8.395%	$247.1081	$247.11	$247.10	$247.10
Purchase #5	$55.25	11.474%	$61.5894	$61.59	$61.60	$61.60
Purchase #6	$34.55	9.807%	$37.9383	$37.94	$37.95	$37.90
Purchase #7	$72.25	8.416%	$78.3306	$78.33	$78.35	$78.30
7 purchase totals =	$709.37		$776.6283	$776.63	$776.65	$776.50