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	$83.51	7.663%	$89.9094	$89.91	$89.90	$89.90
Purchase #2	$93.25	11.687%	$104.1481	$104.15	$104.15	$104.10
Purchase #3	$94.38	6.246%	$100.275	$100.28	$100.30	$100.30
Purchase #4	$23.88	6.477%	$25.4267	$25.43	$25.45	$25.40
Purchase #5	$86.55	5.486%	$91.2981	$91.30	$91.30	$91.30
Purchase #6	$136.46	9.109%	$148.8901	$148.89	$148.90	$148.90
Purchase #7	$182.43	11.505%	$203.4186	$203.42	$203.40	$203.40
7 purchase totals =	$700.46		$763.3660	$763.38	$763.40	$763.30