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	$134.78	3.310%	$139.2412	$139.24	$139.25	$139.20
Purchase #2	$186.79	5.412%	$196.8991	$196.90	$196.90	$196.90
Purchase #3	$39.93	8.298%	$43.2434	$43.24	$43.25	$43.20
Purchase #4	$97.66	7.507%	$104.9913	$104.99	$105.00	$105.00
Purchase #5	$165.92	13.798%	$188.8136	$188.81	$188.80	$188.80
Purchase #6	$26.60	8.559%	$28.8767	$28.88	$28.90	$28.90
Purchase #7	$34.95	7.159%	$37.4521	$37.45	$37.45	$37.50
7 purchase totals =	$686.63		$739.5174	$739.51	$739.55	$739.50