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	$178.46	11.148%	$198.3547	$198.35	$198.35	$198.40
Purchase #2	$177.97	12.330%	$199.9137	$199.91	$199.90	$199.90
Purchase #3	$71.51	9.734%	$78.4708	$78.47	$78.45	$78.50
Purchase #4	$128.68	9.415%	$140.7952	$140.80	$140.80	$140.80
Purchase #5	$19.96	8.208%	$21.5983	$21.60	$21.60	$21.60
Purchase #6	$72.82	5.269%	$76.6569	$76.66	$76.65	$76.70
Purchase #7	$6.89	3.858%	$7.1558	$7.16	$7.15	$7.20
7 purchase totals =	$656.29		$722.9454	$722.95	$722.90	$723.10