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	$50.38	8.744%	$54.7852	$54.79	$54.80	$54.80
Purchase #2	$53.25	11.631%	$59.4435	$59.44	$59.45	$59.40
Purchase #3	$106.46	3.821%	$110.5278	$110.53	$110.55	$110.50
Purchase #4	$234.53	9.507%	$256.8268	$256.83	$256.85	$256.80
Purchase #5	$33.59	13.858%	$38.2449	$38.24	$38.25	$38.20
Purchase #6	$37.63	3.751%	$39.0415	$39.04	$39.05	$39.00
Purchase #7	$85.73	11.161%	$95.2983	$95.30	$95.30	$95.30
7 purchase totals =	$601.57		$654.1680	$654.17	$654.25	$654.00