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	$30.61	6.514%	$32.6039	$32.60	$32.60	$32.60
Purchase #2	$92.60	7.753%	$99.7793	$99.78	$99.80	$99.80
Purchase #3	$78.96	10.513%	$87.2611	$87.26	$87.25	$87.30
Purchase #4	$227.96	5.333%	$240.1171	$240.12	$240.10	$240.10
Purchase #5	$196.63	9.448%	$215.2076	$215.21	$215.20	$215.20
Purchase #6	$164.70	6.815%	$175.9243	$175.92	$175.90	$175.90
Purchase #7	$224.28	13.709%	$255.0265	$255.03	$255.05	$255.00
7 purchase totals =	$1,015.74		$1,105.9198	$1,105.92	$1,105.90	$1,105.90