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	$29.45	8.277%	$31.8876	$31.89	$31.90	$31.90
Purchase #2	$59.69	12.840%	$67.3542	$67.35	$67.35	$67.40
Purchase #3	$222.29	9.292%	$242.9452	$242.95	$242.95	$242.90
Purchase #4	$186.77	6.392%	$198.7083	$198.71	$198.70	$198.70
Purchase #5	$245.82	11.753%	$274.7112	$274.71	$274.70	$274.70
Purchase #6	$154.71	10.815%	$171.4419	$171.44	$171.45	$171.40
Purchase #7	$138.67	11.742%	$154.9526	$154.95	$154.95	$155.00
7 purchase totals =	$1,037.40		$1,142.0010	$1,142.00	$1,142.00	$1,142.00