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	$79.32	13.852%	$90.3074	$90.31	$90.30	$90.30
Purchase #2	$207.58	4.302%	$216.5101	$216.51	$216.50	$216.50
Purchase #3	$178.32	7.441%	$191.5888	$191.59	$191.60	$191.60
Purchase #4	$17.93	13.329%	$20.3199	$20.32	$20.30	$20.30
Purchase #5	$131.67	6.738%	$140.5419	$140.54	$140.55	$140.50
Purchase #6	$233.64	4.651%	$244.5066	$244.51	$244.50	$244.50
Purchase #7	$38.26	6.661%	$40.8085	$40.81	$40.80	$40.80
7 purchase totals =	$886.72		$944.5832	$944.59	$944.55	$944.50