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	$127.78	11.405%	$142.3533	$142.35	$142.35	$142.40
Purchase #2	$162.64	13.657%	$184.8517	$184.85	$184.85	$184.90
Purchase #3	$113.31	8.623%	$123.0807	$123.08	$123.10	$123.10
Purchase #4	$213.56	12.759%	$240.8081	$240.81	$240.80	$240.80
Purchase #5	$177.90	13.530%	$201.9699	$201.97	$201.95	$202.00
Purchase #6	$230.33	10.282%	$254.0125	$254.01	$254.00	$254.00
Purchase #7	$31.45	4.740%	$32.9407	$32.94	$32.95	$32.90
7 purchase totals =	$1,056.97		$1,180.0169	$1,180.01	$1,180.00	$1,180.10