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	$91.90	12.830%	$103.6908	$103.69	$103.70	$103.70
Purchase #2	$199.25	12.167%	$223.4927	$223.49	$223.50	$223.50
Purchase #3	$246.85	10.380%	$272.473	$272.47	$272.45	$272.50
Purchase #4	$79.38	5.764%	$83.9555	$83.96	$83.95	$84.00
Purchase #5	$149.60	7.517%	$160.8454	$160.85	$160.85	$160.80
Purchase #6	$120.30	9.317%	$131.5084	$131.51	$131.50	$131.50
Purchase #7	$57.53	7.836%	$62.0381	$62.04	$62.05	$62.00
7 purchase totals =	$944.81		$1,038.0039	$1,038.01	$1,038.00	$1,038.00