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	$42.70	7.102%	$45.7326	$45.73	$45.75	$45.70
Purchase #2	$99.57	13.498%	$113.01	$113.01	$113.00	$113.00
Purchase #3	$137.30	4.366%	$143.2945	$143.29	$143.30	$143.30
Purchase #4	$131.72	8.757%	$143.2547	$143.25	$143.25	$143.30
Purchase #5	$72.82	4.305%	$75.9549	$75.95	$75.95	$76.00
Purchase #6	$249.39	7.863%	$268.9995	$269.00	$269.00	$269.00
Purchase #7	$196.41	11.778%	$219.5432	$219.54	$219.55	$219.50
7 purchase totals =	$929.91		$1,009.7894	$1,009.77	$1,009.80	$1,009.80