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	$14.55	5.865%	$15.4034	$15.40	$15.40	$15.40
Purchase #2	$88.42	13.248%	$100.1339	$100.13	$100.15	$100.10
Purchase #3	$165.48	13.688%	$188.1309	$188.13	$188.15	$188.10
Purchase #4	$201.77	7.685%	$217.276	$217.28	$217.30	$217.30
Purchase #5	$28.95	9.307%	$31.6444	$31.64	$31.65	$31.60
Purchase #6	$192.69	13.365%	$218.443	$218.44	$218.45	$218.40
Purchase #7	$101.69	7.524%	$109.3412	$109.34	$109.35	$109.30
7 purchase totals =	$793.55		$880.3728	$880.36	$880.45	$880.20