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	$140.29	9.426%	$153.5137	$153.51	$153.50	$153.50
Purchase #2	$161.40	8.152%	$174.5573	$174.56	$174.55	$174.60
Purchase #3	$79.92	12.740%	$90.1018	$90.10	$90.10	$90.10
Purchase #4	$220.65	13.858%	$251.2277	$251.23	$251.25	$251.20
Purchase #5	$180.27	9.258%	$196.9594	$196.96	$196.95	$197.00
Purchase #6	$79.76	3.237%	$82.3418	$82.34	$82.35	$82.30
Purchase #7	$147.65	3.744%	$153.178	$153.18	$153.20	$153.20
7 purchase totals =	$1,009.94		$1,101.8797	$1,101.88	$1,101.90	$1,101.90