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	$134.66	13.280%	$152.5428	$152.54	$152.55	$152.50
Purchase #2	$211.91	3.147%	$218.5788	$218.58	$218.60	$218.60
Purchase #3	$118.96	4.599%	$124.431	$124.43	$124.45	$124.40
Purchase #4	$41.59	4.632%	$43.5164	$43.52	$43.50	$43.50
Purchase #5	$180.26	12.316%	$202.4608	$202.46	$202.45	$202.50
Purchase #6	$78.60	5.823%	$83.1769	$83.18	$83.20	$83.20
Purchase #7	$44.82	11.752%	$50.0872	$50.09	$50.10	$50.10
7 purchase totals =	$810.80		$874.7939	$874.80	$874.85	$874.80