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	$37.98	6.649%	$40.5053	$40.51	$40.50	$40.50
Purchase #2	$139.34	9.111%	$152.0353	$152.04	$152.05	$152.00
Purchase #3	$103.25	5.824%	$109.2633	$109.26	$109.25	$109.30
Purchase #4	$230.69	4.357%	$240.7412	$240.74	$240.75	$240.70
Purchase #5	$139.81	13.775%	$159.0688	$159.07	$159.05	$159.10
Purchase #6	$102.41	3.279%	$105.768	$105.77	$105.75	$105.80
Purchase #7	$172.83	5.596%	$182.5016	$182.50	$182.50	$182.50
7 purchase totals =	$926.31		$989.8835	$989.89	$989.85	$989.90