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	$125.61	10.602%	$138.9272	$138.93	$138.95	$138.90
Purchase #2	$52.35	12.865%	$59.0848	$59.08	$59.10	$59.10
Purchase #3	$127.62	9.665%	$139.9545	$139.95	$139.95	$140.00
Purchase #4	$93.88	11.290%	$104.4791	$104.48	$104.50	$104.50
Purchase #5	$57.32	8.443%	$62.1595	$62.16	$62.15	$62.20
Purchase #6	$216.33	5.539%	$228.3125	$228.31	$228.30	$228.30
Purchase #7	$244.53	12.144%	$274.2257	$274.23	$274.25	$274.20
7 purchase totals =	$917.64		$1,007.1433	$1,007.14	$1,007.20	$1,007.20