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	$110.78	11.454%	$123.4687	$123.47	$123.45	$123.50
Purchase #2	$57.57	6.242%	$61.1635	$61.16	$61.15	$61.20
Purchase #3	$122.34	12.147%	$137.2006	$137.20	$137.20	$137.20
Purchase #4	$37.73	5.687%	$39.8757	$39.88	$39.90	$39.90
Purchase #5	$154.44	9.363%	$168.9002	$168.90	$168.90	$168.90
Purchase #6	$234.29	12.818%	$264.3213	$264.32	$264.30	$264.30
Purchase #7	$171.27	7.569%	$184.2334	$184.23	$184.25	$184.20
7 purchase totals =	$888.42		$979.1634	$979.16	$979.15	$979.20