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	$249.38	10.188%	$274.7868	$274.79	$274.80	$274.80
Purchase #2	$179.93	9.803%	$197.5685	$197.57	$197.55	$197.60
Purchase #3	$90.33	11.373%	$100.6032	$100.60	$100.60	$100.60
Purchase #4	$243.52	11.586%	$271.7342	$271.73	$271.75	$271.70
Purchase #5	$132.96	4.787%	$139.3248	$139.32	$139.30	$139.30
Purchase #6	$59.90	9.725%	$65.7253	$65.73	$65.75	$65.70
Purchase #7	$126.55	12.240%	$142.0397	$142.04	$142.05	$142.00
7 purchase totals =	$1,082.57		$1,191.7825	$1,191.78	$1,191.80	$1,191.70