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	$29.71	4.821%	$31.1423	$31.14	$31.15	$31.10
Purchase #2	$59.98	3.715%	$62.2083	$62.21	$62.20	$62.20
Purchase #3	$73.94	5.663%	$78.1272	$78.13	$78.15	$78.10
Purchase #4	$52.33	9.158%	$57.1224	$57.12	$57.10	$57.10
Purchase #5	$8.82	12.581%	$9.9296	$9.93	$9.95	$9.90
Purchase #6	$132.53	7.817%	$142.8899	$142.89	$142.90	$142.90
Purchase #7	$103.59	5.264%	$109.043	$109.04	$109.05	$109.00
7 purchase totals =	$460.90		$490.4627	$490.46	$490.50	$490.30