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	$53.69	10.274%	$59.2061	$59.21	$59.20	$59.20
Purchase #2	$199.84	5.545%	$210.9211	$210.92	$210.90	$210.90
Purchase #3	$64.93	8.350%	$70.3517	$70.35	$70.35	$70.40
Purchase #4	$105.34	4.342%	$109.9139	$109.91	$109.90	$109.90
Purchase #5	$23.55	10.271%	$25.9688	$25.97	$25.95	$26.00
Purchase #6	$124.57	13.676%	$141.6062	$141.61	$141.60	$141.60
Purchase #7	$54.93	7.801%	$59.2151	$59.22	$59.20	$59.20
7 purchase totals =	$626.85		$677.1829	$677.19	$677.10	$677.20