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	$52.36	13.333%	$59.3412	$59.34	$59.35	$59.30
Purchase #2	$103.26	10.317%	$113.9133	$113.91	$113.90	$113.90
Purchase #3	$6.73	12.517%	$7.5724	$7.57	$7.55	$7.60
Purchase #4	$153.60	10.137%	$169.1704	$169.17	$169.15	$169.20
Purchase #5	$59.82	10.476%	$66.0867	$66.09	$66.10	$66.10
Purchase #6	$84.47	13.730%	$96.0677	$96.07	$96.05	$96.10
Purchase #7	$80.76	6.251%	$85.8083	$85.81	$85.80	$85.80
7 purchase totals =	$541.00		$597.9600	$597.96	$597.90	$598.00