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	$16.47	11.514%	$18.3664	$18.37	$18.35	$18.40
Purchase #2	$217.42	12.197%	$243.9387	$243.94	$243.95	$243.90
Purchase #3	$157.46	10.844%	$174.535	$174.54	$174.55	$174.50
Purchase #4	$154.84	8.172%	$167.4935	$167.49	$167.50	$167.50
Purchase #5	$104.26	5.436%	$109.9276	$109.93	$109.95	$109.90
Purchase #6	$96.31	12.297%	$108.1532	$108.15	$108.15	$108.20
Purchase #7	$60.73	10.365%	$67.0247	$67.02	$67.00	$67.00
7 purchase totals =	$807.49		$889.4391	$889.44	$889.45	$889.40