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	$37.47	6.442%	$39.8838	$39.88	$39.90	$39.90
Purchase #2	$50.73	8.730%	$55.1587	$55.16	$55.15	$55.20
Purchase #3	$63.79	5.534%	$67.3201	$67.32	$67.30	$67.30
Purchase #4	$76.49	6.173%	$81.2117	$81.21	$81.20	$81.20
Purchase #5	$223.76	3.435%	$231.4462	$231.45	$231.45	$231.40
Purchase #6	$182.30	4.367%	$190.261	$190.26	$190.25	$190.30
Purchase #7	$104.51	4.594%	$109.3112	$109.31	$109.30	$109.30
7 purchase totals =	$739.05		$774.5927	$774.59	$774.55	$774.60