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	$84.69	6.719%	$90.3803	$90.38	$90.40	$90.40
Purchase #2	$207.66	8.309%	$224.9145	$224.91	$224.90	$224.90
Purchase #3	$232.85	4.390%	$243.0721	$243.07	$243.05	$243.10
Purchase #4	$140.40	10.245%	$154.784	$154.78	$154.80	$154.80
Purchase #5	$80.72	12.208%	$90.5743	$90.57	$90.55	$90.60
Purchase #6	$215.88	10.476%	$238.4956	$238.50	$238.50	$238.50
Purchase #7	$28.77	9.520%	$31.5089	$31.51	$31.50	$31.50
7 purchase totals =	$990.97		$1,073.7297	$1,073.72	$1,073.70	$1,073.80