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	$131.67	3.786%	$136.655	$136.66	$136.65	$136.70
Purchase #2	$233.50	12.825%	$263.4464	$263.45	$263.45	$263.40
Purchase #3	$7.95	11.732%	$8.8827	$8.88	$8.90	$8.90
Purchase #4	$168.55	12.394%	$189.4401	$189.44	$189.45	$189.40
Purchase #5	$19.82	8.508%	$21.5063	$21.51	$21.50	$21.50
Purchase #6	$108.72	5.444%	$114.6387	$114.64	$114.65	$114.60
Purchase #7	$79.73	7.173%	$85.449	$85.45	$85.45	$85.40
7 purchase totals =	$749.94		$820.0182	$820.03	$820.05	$819.90