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	$36.91	10.797%	$40.8952	$40.90	$40.90	$40.90
Purchase #2	$181.93	11.753%	$203.3122	$203.31	$203.30	$203.30
Purchase #3	$97.82	12.762%	$110.3038	$110.30	$110.30	$110.30
Purchase #4	$240.37	3.789%	$249.4776	$249.48	$249.50	$249.50
Purchase #5	$66.47	10.487%	$73.4407	$73.44	$73.45	$73.40
Purchase #6	$195.41	12.244%	$219.336	$219.34	$219.35	$219.30
Purchase #7	$65.34	10.797%	$72.3948	$72.39	$72.40	$72.40
7 purchase totals =	$884.25		$969.1603	$969.16	$969.20	$969.10