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	$112.56	10.371%	$124.2336	$124.23	$124.25	$124.20
Purchase #2	$189.69	13.191%	$214.712	$214.71	$214.70	$214.70
Purchase #3	$192.33	10.170%	$211.89	$211.89	$211.90	$211.90
Purchase #4	$40.85	12.196%	$45.8321	$45.83	$45.85	$45.80
Purchase #5	$114.93	9.488%	$125.8346	$125.83	$125.85	$125.80
Purchase #6	$54.54	9.874%	$59.9253	$59.93	$59.95	$59.90
Purchase #7	$55.81	13.822%	$63.5241	$63.52	$63.50	$63.50
7 purchase totals =	$760.71		$845.9517	$845.94	$846.00	$845.80