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	$35.56	10.310%	$39.2262	$39.23	$39.25	$39.20
Purchase #2	$157.29	9.729%	$172.5927	$172.59	$172.60	$172.60
Purchase #3	$148.67	12.510%	$167.2686	$167.27	$167.25	$167.30
Purchase #4	$19.85	5.229%	$20.888	$20.89	$20.90	$20.90
Purchase #5	$154.76	8.658%	$168.1591	$168.16	$168.15	$168.20
Purchase #6	$125.83	9.314%	$137.5498	$137.55	$137.55	$137.50
Purchase #7	$40.38	12.624%	$45.4776	$45.48	$45.50	$45.50
7 purchase totals =	$682.34		$751.1620	$751.17	$751.20	$751.20