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	$37.95	4.321%	$39.5898	$39.59	$39.60	$39.60
Purchase #2	$225.73	7.377%	$242.3821	$242.38	$242.40	$242.40
Purchase #3	$209.77	5.515%	$221.3388	$221.34	$221.35	$221.30
Purchase #4	$36.48	12.620%	$41.0838	$41.08	$41.10	$41.10
Purchase #5	$111.70	10.692%	$123.643	$123.64	$123.65	$123.60
Purchase #6	$62.35	5.201%	$65.5928	$65.59	$65.60	$65.60
Purchase #7	$93.54	12.479%	$105.2129	$105.21	$105.20	$105.20
7 purchase totals =	$777.52		$838.8432	$838.83	$838.90	$838.80