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	$99.49	5.781%	$105.2415	$105.24	$105.25	$105.20
Purchase #2	$91.91	4.868%	$96.3842	$96.38	$96.40	$96.40
Purchase #3	$98.88	3.801%	$102.6384	$102.64	$102.65	$102.60
Purchase #4	$32.36	12.623%	$36.4448	$36.44	$36.45	$36.40
Purchase #5	$162.55	11.310%	$180.9344	$180.93	$180.95	$180.90
Purchase #6	$18.88	5.222%	$19.8659	$19.87	$19.85	$19.90
Purchase #7	$118.55	11.252%	$131.8892	$131.89	$131.90	$131.90
7 purchase totals =	$622.62		$673.3984	$673.39	$673.45	$673.30