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	$71.77	9.402%	$78.5178	$78.52	$78.50	$78.50
Purchase #2	$53.91	9.734%	$59.1576	$59.16	$59.15	$59.20
Purchase #3	$168.54	13.111%	$190.6373	$190.64	$190.65	$190.60
Purchase #4	$130.62	10.385%	$144.1849	$144.18	$144.20	$144.20
Purchase #5	$163.59	9.512%	$179.1507	$179.15	$179.15	$179.20
Purchase #6	$72.58	5.449%	$76.5349	$76.53	$76.55	$76.50
Purchase #7	$112.77	10.513%	$124.6255	$124.63	$124.65	$124.60
7 purchase totals =	$773.78		$852.8087	$852.81	$852.85	$852.80