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	$131.76	4.706%	$137.9606	$137.96	$137.95	$138.00
Purchase #2	$141.68	6.295%	$150.5988	$150.60	$150.60	$150.60
Purchase #3	$159.33	5.455%	$168.0215	$168.02	$168.00	$168.00
Purchase #4	$36.57	12.449%	$41.1226	$41.12	$41.10	$41.10
Purchase #5	$140.61	12.567%	$158.2805	$158.28	$158.30	$158.30
Purchase #6	$62.71	13.644%	$71.2662	$71.27	$71.25	$71.30
Purchase #7	$51.94	11.566%	$57.9474	$57.95	$57.95	$57.90
7 purchase totals =	$724.60		$785.1976	$785.20	$785.15	$785.20