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	$213.76	3.451%	$221.1369	$221.14	$221.15	$221.10
Purchase #2	$209.39	11.695%	$233.8782	$233.88	$233.90	$233.90
Purchase #3	$147.59	5.812%	$156.1679	$156.17	$156.15	$156.20
Purchase #4	$18.96	11.623%	$21.1637	$21.16	$21.15	$21.20
Purchase #5	$89.35	9.570%	$97.9008	$97.90	$97.90	$97.90
Purchase #6	$5.95	13.607%	$6.7596	$6.76	$6.75	$6.80
Purchase #7	$97.59	9.457%	$106.8191	$106.82	$106.80	$106.80
7 purchase totals =	$782.59		$843.8262	$843.83	$843.80	$843.90