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	$39.99	6.364%	$42.535	$42.54	$42.55	$42.50
Purchase #2	$226.73	3.257%	$234.1146	$234.11	$234.10	$234.10
Purchase #3	$59.66	4.267%	$62.2057	$62.21	$62.20	$62.20
Purchase #4	$152.45	4.181%	$158.8239	$158.82	$158.80	$158.80
Purchase #5	$141.87	11.607%	$158.3369	$158.34	$158.35	$158.30
Purchase #6	$67.38	8.466%	$73.0844	$73.08	$73.10	$73.10
Purchase #7	$140.76	8.241%	$152.36	$152.36	$152.35	$152.40
7 purchase totals =	$828.84		$881.4605	$881.46	$881.45	$881.40