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	$170.36	4.415%	$177.8814	$177.88	$177.90	$177.90
Purchase #2	$130.44	10.123%	$143.6444	$143.64	$143.65	$143.60
Purchase #3	$72.69	7.791%	$78.3533	$78.35	$78.35	$78.40
Purchase #4	$206.40	7.393%	$221.6592	$221.66	$221.65	$221.70
Purchase #5	$153.88	6.188%	$163.4021	$163.40	$163.40	$163.40
Purchase #6	$215.82	3.672%	$223.7449	$223.74	$223.75	$223.70
Purchase #7	$85.52	7.449%	$91.8904	$91.89	$91.90	$91.90
7 purchase totals =	$1,035.11		$1,100.5757	$1,100.56	$1,100.60	$1,100.60