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	$122.25	12.339%	$137.3344	$137.33	$137.35	$137.30
Purchase #2	$139.94	9.842%	$153.7129	$153.71	$153.70	$153.70
Purchase #3	$78.96	3.707%	$81.887	$81.89	$81.90	$81.90
Purchase #4	$249.84	9.306%	$273.0901	$273.09	$273.10	$273.10
Purchase #5	$71.33	8.402%	$77.3231	$77.32	$77.30	$77.30
Purchase #6	$92.47	7.557%	$99.458	$99.46	$99.45	$99.50
Purchase #7	$157.43	12.214%	$176.6585	$176.66	$176.65	$176.70
7 purchase totals =	$912.22		$999.4640	$999.46	$999.45	$999.50