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	$43.52	3.664%	$45.1146	$45.11	$45.10	$45.10
Purchase #2	$37.37	10.334%	$41.2318	$41.23	$41.25	$41.20
Purchase #3	$40.77	13.740%	$46.3718	$46.37	$46.35	$46.40
Purchase #4	$50.90	8.600%	$55.2774	$55.28	$55.30	$55.30
Purchase #5	$83.86	10.771%	$92.8926	$92.89	$92.90	$92.90
Purchase #6	$228.69	9.810%	$251.1245	$251.12	$251.10	$251.10
Purchase #7	$102.65	12.553%	$115.5357	$115.54	$115.55	$115.50
7 purchase totals =	$587.76		$647.5484	$647.54	$647.55	$647.50