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	$74.40	10.437%	$82.1651	$82.17	$82.15	$82.20
Purchase #2	$94.52	12.789%	$106.6082	$106.61	$106.60	$106.60
Purchase #3	$6.29	8.530%	$6.8265	$6.83	$6.85	$6.80
Purchase #4	$233.73	13.596%	$265.5079	$265.51	$265.50	$265.50
Purchase #5	$5.34	6.108%	$5.6662	$5.67	$5.65	$5.70
Purchase #6	$29.64	6.499%	$31.5663	$31.57	$31.55	$31.60
Purchase #7	$90.95	9.871%	$99.9277	$99.93	$99.95	$99.90
7 purchase totals =	$534.87		$598.2679	$598.29	$598.25	$598.30