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	$35.42	9.661%	$38.8419	$38.84	$38.85	$38.80
Purchase #2	$45.91	3.368%	$47.4562	$47.46	$47.45	$47.50
Purchase #3	$117.25	12.421%	$131.8136	$131.81	$131.80	$131.80
Purchase #4	$32.49	8.188%	$35.1503	$35.15	$35.15	$35.20
Purchase #5	$232.64	9.326%	$254.336	$254.34	$254.35	$254.30
Purchase #6	$30.57	6.270%	$32.4867	$32.49	$32.50	$32.50
Purchase #7	$188.57	12.650%	$212.4241	$212.42	$212.40	$212.40
7 purchase totals =	$682.85		$752.5088	$752.51	$752.50	$752.50