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	$15.87	10.321%	$17.5079	$17.51	$17.50	$17.50
Purchase #2	$176.69	10.334%	$194.9491	$194.95	$194.95	$194.90
Purchase #3	$242.63	13.710%	$275.8946	$275.89	$275.90	$275.90
Purchase #4	$120.47	9.250%	$131.6135	$131.61	$131.60	$131.60
Purchase #5	$149.54	9.682%	$164.0185	$164.02	$164.00	$164.00
Purchase #6	$119.98	3.450%	$124.1193	$124.12	$124.10	$124.10
Purchase #7	$189.36	3.718%	$196.4004	$196.40	$196.40	$196.40
7 purchase totals =	$1,014.54		$1,104.5033	$1,104.50	$1,104.45	$1,104.40