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	$53.35	11.661%	$59.5711	$59.57	$59.55	$59.60
Purchase #2	$232.93	12.210%	$261.3708	$261.37	$261.35	$261.40
Purchase #3	$147.36	5.722%	$155.7919	$155.79	$155.80	$155.80
Purchase #4	$54.79	9.651%	$60.0778	$60.08	$60.10	$60.10
Purchase #5	$169.41	5.874%	$179.3611	$179.36	$179.35	$179.40
Purchase #6	$98.36	13.769%	$111.9032	$111.90	$111.90	$111.90
Purchase #7	$29.26	6.316%	$31.1081	$31.11	$31.10	$31.10
7 purchase totals =	$785.46		$859.1840	$859.18	$859.15	$859.30