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	$178.54	12.319%	$200.5343	$200.53	$200.55	$200.50
Purchase #2	$53.27	9.201%	$58.1714	$58.17	$58.15	$58.20
Purchase #3	$41.33	6.300%	$43.9338	$43.93	$43.95	$43.90
Purchase #4	$41.25	3.515%	$42.6999	$42.70	$42.70	$42.70
Purchase #5	$99.51	5.110%	$104.595	$104.60	$104.60	$104.60
Purchase #6	$140.47	9.637%	$154.0071	$154.01	$154.00	$154.00
Purchase #7	$51.49	11.689%	$57.5087	$57.51	$57.50	$57.50
7 purchase totals =	$605.86		$661.4502	$661.45	$661.45	$661.40