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	$37.48	12.224%	$42.0616	$42.06	$42.05	$42.10
Purchase #2	$30.74	6.623%	$32.7759	$32.78	$32.80	$32.80
Purchase #3	$19.30	5.285%	$20.32	$20.32	$20.30	$20.30
Purchase #4	$234.63	5.410%	$247.3235	$247.32	$247.30	$247.30
Purchase #5	$72.48	8.625%	$78.7314	$78.73	$78.75	$78.70
Purchase #6	$100.59	8.683%	$109.3242	$109.32	$109.30	$109.30
Purchase #7	$37.31	4.346%	$38.9315	$38.93	$38.95	$38.90
7 purchase totals =	$532.53		$569.4681	$569.46	$569.45	$569.40