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	$220.93	3.725%	$229.1596	$229.16	$229.15	$229.20
Purchase #2	$230.47	8.702%	$250.5255	$250.53	$250.55	$250.50
Purchase #3	$218.56	10.241%	$240.9427	$240.94	$240.95	$240.90
Purchase #4	$104.29	4.406%	$108.885	$108.89	$108.90	$108.90
Purchase #5	$242.84	13.465%	$275.5384	$275.54	$275.55	$275.50
Purchase #6	$85.81	5.344%	$90.3957	$90.40	$90.40	$90.40
Purchase #7	$160.83	10.351%	$177.4775	$177.48	$177.50	$177.50
7 purchase totals =	$1,263.73		$1,372.9244	$1,372.94	$1,373.00	$1,372.90