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	$115.97	10.391%	$128.0204	$128.02	$128.00	$128.00
Purchase #2	$158.71	6.437%	$168.9262	$168.93	$168.95	$168.90
Purchase #3	$108.57	13.590%	$123.3247	$123.32	$123.30	$123.30
Purchase #4	$88.39	10.334%	$97.5242	$97.52	$97.50	$97.50
Purchase #5	$35.71	11.563%	$39.8391	$39.84	$39.85	$39.80
Purchase #6	$231.76	3.731%	$240.407	$240.41	$240.40	$240.40
Purchase #7	$59.87	8.781%	$65.1272	$65.13	$65.15	$65.10
7 purchase totals =	$798.98		$863.1688	$863.17	$863.15	$863.00