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	$80.90	6.120%	$85.8511	$85.85	$85.85	$85.90
Purchase #2	$115.66	7.110%	$123.8834	$123.88	$123.90	$123.90
Purchase #3	$46.82	8.614%	$50.8531	$50.85	$50.85	$50.90
Purchase #4	$42.75	3.148%	$44.0958	$44.10	$44.10	$44.10
Purchase #5	$163.91	12.436%	$184.2938	$184.29	$184.30	$184.30
Purchase #6	$127.76	10.651%	$141.3677	$141.37	$141.35	$141.40
Purchase #7	$244.81	8.234%	$264.9677	$264.97	$264.95	$265.00
7 purchase totals =	$822.61		$895.3126	$895.31	$895.30	$895.50