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	$68.96	3.693%	$71.5067	$71.51	$71.50	$71.50
Purchase #2	$136.77	5.586%	$144.41	$144.41	$144.40	$144.40
Purchase #3	$51.79	3.822%	$53.7694	$53.77	$53.75	$53.80
Purchase #4	$57.90	3.435%	$59.8889	$59.89	$59.90	$59.90
Purchase #5	$39.43	13.384%	$44.7073	$44.71	$44.70	$44.70
Purchase #6	$61.56	8.756%	$66.9502	$66.95	$66.95	$67.00
Purchase #7	$109.73	9.381%	$120.0238	$120.02	$120.00	$120.00
7 purchase totals =	$526.14		$561.2563	$561.26	$561.20	$561.30