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	$47.55	7.152%	$50.9508	$50.95	$50.95	$51.00
Purchase #2	$140.85	13.853%	$160.362	$160.36	$160.35	$160.40
Purchase #3	$81.77	11.249%	$90.9683	$90.97	$90.95	$91.00
Purchase #4	$45.98	5.243%	$48.3907	$48.39	$48.40	$48.40
Purchase #5	$105.91	12.571%	$119.2239	$119.22	$119.20	$119.20
Purchase #6	$124.51	11.647%	$139.0117	$139.01	$139.00	$139.00
Purchase #7	$199.92	5.869%	$211.6533	$211.65	$211.65	$211.70
7 purchase totals =	$746.49		$820.5607	$820.55	$820.50	$820.70