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	$189.55	3.747%	$196.6524	$196.65	$196.65	$196.70
Purchase #2	$62.63	4.685%	$65.5642	$65.56	$65.55	$65.60
Purchase #3	$144.43	3.774%	$149.8808	$149.88	$149.90	$149.90
Purchase #4	$216.48	4.169%	$225.5051	$225.51	$225.50	$225.50
Purchase #5	$120.74	13.111%	$136.5702	$136.57	$136.55	$136.60
Purchase #6	$225.66	6.627%	$240.6145	$240.61	$240.60	$240.60
Purchase #7	$237.26	13.873%	$270.1751	$270.18	$270.20	$270.20
7 purchase totals =	$1,196.75		$1,284.9623	$1,284.96	$1,284.95	$1,285.10