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	$42.36	9.799%	$46.5109	$46.51	$46.50	$46.50
Purchase #2	$92.57	11.663%	$103.3664	$103.37	$103.35	$103.40
Purchase #3	$96.78	6.385%	$102.9594	$102.96	$102.95	$103.00
Purchase #4	$92.78	11.318%	$103.2808	$103.28	$103.30	$103.30
Purchase #5	$234.66	12.320%	$263.5701	$263.57	$263.55	$263.60
Purchase #6	$23.82	8.619%	$25.873	$25.87	$25.85	$25.90
Purchase #7	$167.83	6.831%	$179.2945	$179.29	$179.30	$179.30
7 purchase totals =	$750.80		$824.8551	$824.85	$824.80	$825.00