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	$219.46	13.805%	$249.7565	$249.76	$249.75	$249.80
Purchase #2	$37.89	13.780%	$43.1112	$43.11	$43.10	$43.10
Purchase #3	$247.51	6.635%	$263.9323	$263.93	$263.95	$263.90
Purchase #4	$70.62	3.287%	$72.9413	$72.94	$72.95	$72.90
Purchase #5	$164.62	8.852%	$179.1922	$179.19	$179.20	$179.20
Purchase #6	$44.51	6.443%	$47.3778	$47.38	$47.40	$47.40
Purchase #7	$80.82	10.715%	$89.4799	$89.48	$89.50	$89.50
7 purchase totals =	$865.43		$945.7912	$945.79	$945.85	$945.80