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	$48.81	7.537%	$52.4888	$52.49	$52.50	$52.50
Purchase #2	$99.73	7.771%	$107.48	$107.48	$107.50	$107.50
Purchase #3	$41.41	5.738%	$43.7861	$43.79	$43.80	$43.80
Purchase #4	$69.29	3.770%	$71.9022	$71.90	$71.90	$71.90
Purchase #5	$16.94	9.239%	$18.5051	$18.51	$18.50	$18.50
Purchase #6	$179.77	12.551%	$202.3329	$202.33	$202.35	$202.30
Purchase #7	$244.38	7.848%	$263.5589	$263.56	$263.55	$263.60
7 purchase totals =	$700.33		$760.0540	$760.06	$760.10	$760.10