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	$189.62	12.273%	$212.8921	$212.89	$212.90	$212.90
Purchase #2	$79.66	4.674%	$83.3833	$83.38	$83.40	$83.40
Purchase #3	$165.45	7.148%	$177.2764	$177.28	$177.30	$177.30
Purchase #4	$183.83	6.820%	$196.3672	$196.37	$196.35	$196.40
Purchase #5	$204.88	5.433%	$216.0111	$216.01	$216.00	$216.00
Purchase #6	$173.58	13.245%	$196.5707	$196.57	$196.55	$196.60
Purchase #7	$239.49	5.711%	$253.1673	$253.17	$253.15	$253.20
7 purchase totals =	$1,236.51		$1,335.6681	$1,335.67	$1,335.65	$1,335.80