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	$37.78	8.330%	$40.9271	$40.93	$40.95	$40.90
Purchase #2	$51.56	8.538%	$55.9622	$55.96	$55.95	$56.00
Purchase #3	$114.29	8.217%	$123.6812	$123.68	$123.70	$123.70
Purchase #4	$72.28	10.144%	$79.6121	$79.61	$79.60	$79.60
Purchase #5	$66.60	8.782%	$72.4488	$72.45	$72.45	$72.40
Purchase #6	$192.64	12.198%	$216.1382	$216.14	$216.15	$216.10
Purchase #7	$158.94	13.319%	$180.1092	$180.11	$180.10	$180.10
7 purchase totals =	$694.09		$768.8788	$768.88	$768.90	$768.80