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	$17.36	6.350%	$18.4624	$18.46	$18.45	$18.50
Purchase #2	$55.51	6.360%	$59.0404	$59.04	$59.05	$59.00
Purchase #3	$39.52	12.522%	$44.4687	$44.47	$44.45	$44.50
Purchase #4	$149.90	11.755%	$167.5207	$167.52	$167.50	$167.50
Purchase #5	$18.71	4.447%	$19.542	$19.54	$19.55	$19.50
Purchase #6	$119.46	3.766%	$123.9589	$123.96	$123.95	$124.00
Purchase #7	$104.32	12.171%	$117.0168	$117.02	$117.00	$117.00
7 purchase totals =	$504.78		$550.0099	$550.01	$549.95	$550.00