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	$119.31	7.683%	$128.4766	$128.48	$128.50	$128.50
Purchase #2	$123.57	11.222%	$137.437	$137.44	$137.45	$137.40
Purchase #3	$162.30	13.560%	$184.3079	$184.31	$184.30	$184.30
Purchase #4	$31.77	8.204%	$34.3764	$34.38	$34.40	$34.40
Purchase #5	$246.50	3.224%	$254.4472	$254.45	$254.45	$254.40
Purchase #6	$27.76	5.305%	$29.2327	$29.23	$29.25	$29.20
Purchase #7	$155.32	12.364%	$174.5238	$174.52	$174.50	$174.50
7 purchase totals =	$866.53		$942.8016	$942.81	$942.85	$942.70