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	$131.79	7.591%	$141.7942	$141.79	$141.80	$141.80
Purchase #2	$116.36	6.431%	$123.8431	$123.84	$123.85	$123.80
Purchase #3	$39.61	9.817%	$43.4985	$43.50	$43.50	$43.50
Purchase #4	$102.72	5.348%	$108.2135	$108.21	$108.20	$108.20
Purchase #5	$89.32	11.685%	$99.757	$99.76	$99.75	$99.80
Purchase #6	$90.69	5.218%	$95.4222	$95.42	$95.40	$95.40
Purchase #7	$36.57	3.375%	$37.8042	$37.80	$37.80	$37.80
7 purchase totals =	$607.06		$650.3327	$650.32	$650.30	$650.30