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	$40.39	7.688%	$43.4952	$43.50	$43.50	$43.50
Purchase #2	$133.31	5.830%	$141.082	$141.08	$141.10	$141.10
Purchase #3	$113.44	6.588%	$120.9134	$120.91	$120.90	$120.90
Purchase #4	$222.89	10.765%	$246.8841	$246.88	$246.90	$246.90
Purchase #5	$69.35	11.138%	$77.0742	$77.07	$77.05	$77.10
Purchase #6	$176.70	4.780%	$185.1463	$185.15	$185.15	$185.10
Purchase #7	$5.63	5.578%	$5.944	$5.94	$5.95	$5.90
7 purchase totals =	$761.71		$820.5392	$820.53	$820.55	$820.50