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	$135.39	12.646%	$152.5114	$152.51	$152.50	$152.50
Purchase #2	$160.76	10.547%	$177.7154	$177.72	$177.70	$177.70
Purchase #3	$29.83	3.442%	$30.8567	$30.86	$30.85	$30.90
Purchase #4	$35.92	6.213%	$38.1517	$38.15	$38.15	$38.20
Purchase #5	$37.56	12.625%	$42.302	$42.30	$42.30	$42.30
Purchase #6	$90.64	12.351%	$101.8349	$101.83	$101.85	$101.80
Purchase #7	$50.98	7.505%	$54.806	$54.81	$54.80	$54.80
7 purchase totals =	$541.08		$598.1781	$598.18	$598.15	$598.20