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	$42.67	5.250%	$44.9102	$44.91	$44.90	$44.90
Purchase #2	$113.85	8.803%	$123.8722	$123.87	$123.85	$123.90
Purchase #3	$189.55	10.139%	$208.7685	$208.77	$208.75	$208.80
Purchase #4	$56.48	8.254%	$61.1419	$61.14	$61.15	$61.10
Purchase #5	$168.89	12.464%	$189.9404	$189.94	$189.95	$189.90
Purchase #6	$231.97	11.535%	$258.7277	$258.73	$258.75	$258.70
Purchase #7	$222.83	4.584%	$233.0445	$233.04	$233.05	$233.00
7 purchase totals =	$1,026.24		$1,120.4054	$1,120.40	$1,120.40	$1,120.30