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	$90.36	9.583%	$99.0192	$99.02	$99.00	$99.00
Purchase #2	$211.63	8.214%	$229.0133	$229.01	$229.00	$229.00
Purchase #3	$42.27	7.219%	$45.3215	$45.32	$45.30	$45.30
Purchase #4	$55.79	10.426%	$61.6067	$61.61	$61.60	$61.60
Purchase #5	$37.69	13.581%	$42.8087	$42.81	$42.80	$42.80
Purchase #6	$181.90	8.142%	$196.7103	$196.71	$196.70	$196.70
Purchase #7	$30.38	6.782%	$32.4404	$32.44	$32.45	$32.40
7 purchase totals =	$650.02		$706.9201	$706.92	$706.85	$706.80