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	$40.59	12.815%	$45.7916	$45.79	$45.80	$45.80
Purchase #2	$158.47	6.677%	$169.051	$169.05	$169.05	$169.10
Purchase #3	$226.83	13.176%	$256.7171	$256.72	$256.70	$256.70
Purchase #4	$98.46	7.702%	$106.0434	$106.04	$106.05	$106.00
Purchase #5	$29.86	11.554%	$33.31	$33.31	$33.30	$33.30
Purchase #6	$89.70	3.431%	$92.7776	$92.78	$92.80	$92.80
Purchase #7	$7.73	6.224%	$8.2111	$8.21	$8.20	$8.20
7 purchase totals =	$651.64		$711.9018	$711.90	$711.90	$711.90