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	$250.35	5.211%	$263.3957	$263.40	$263.40	$263.40
Purchase #2	$44.34	8.502%	$48.1098	$48.11	$48.10	$48.10
Purchase #3	$190.46	9.494%	$208.5423	$208.54	$208.55	$208.50
Purchase #4	$181.61	13.487%	$206.1037	$206.10	$206.10	$206.10
Purchase #5	$99.86	5.662%	$105.5141	$105.51	$105.50	$105.50
Purchase #6	$144.66	13.525%	$164.2253	$164.23	$164.25	$164.20
Purchase #7	$55.81	5.759%	$59.0241	$59.02	$59.00	$59.00
7 purchase totals =	$967.09		$1,054.9150	$1,054.91	$1,054.90	$1,054.80