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	$140.55	6.484%	$149.6633	$149.66	$149.65	$149.70
Purchase #2	$159.32	13.384%	$180.6434	$180.64	$180.65	$180.60
Purchase #3	$69.36	12.655%	$78.1375	$78.14	$78.15	$78.10
Purchase #4	$56.46	13.222%	$63.9251	$63.93	$63.95	$63.90
Purchase #5	$23.47	6.835%	$25.0742	$25.07	$25.05	$25.10
Purchase #6	$81.87	9.404%	$89.5691	$89.57	$89.55	$89.60
Purchase #7	$29.56	12.103%	$33.1376	$33.14	$33.15	$33.10
7 purchase totals =	$560.59		$620.1502	$620.15	$620.15	$620.10