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	$123.95	12.544%	$139.4983	$139.50	$139.50	$139.50
Purchase #2	$178.89	12.656%	$201.5303	$201.53	$201.55	$201.50
Purchase #3	$6.86	13.286%	$7.7714	$7.77	$7.75	$7.80
Purchase #4	$243.44	7.821%	$262.4794	$262.48	$262.50	$262.50
Purchase #5	$63.74	6.487%	$67.8748	$67.87	$67.85	$67.90
Purchase #6	$96.82	4.776%	$101.4441	$101.44	$101.45	$101.40
Purchase #7	$56.96	7.850%	$61.4314	$61.43	$61.45	$61.40
7 purchase totals =	$770.66		$842.0297	$842.02	$842.05	$842.00