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	$136.46	3.505%	$141.2429	$141.24	$141.25	$141.20
Purchase #2	$140.80	3.487%	$145.7097	$145.71	$145.70	$145.70
Purchase #3	$60.50	11.665%	$67.5573	$67.56	$67.55	$67.60
Purchase #4	$117.53	7.719%	$126.6021	$126.60	$126.60	$126.60
Purchase #5	$83.36	13.334%	$94.4752	$94.48	$94.50	$94.50
Purchase #6	$98.85	13.589%	$112.2827	$112.28	$112.30	$112.30
Purchase #7	$144.96	4.519%	$151.5107	$151.51	$151.50	$151.50
7 purchase totals =	$782.46		$839.3806	$839.38	$839.40	$839.40