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	$68.77	12.442%	$77.3264	$77.33	$77.35	$77.30
Purchase #2	$183.89	9.166%	$200.7454	$200.75	$200.75	$200.70
Purchase #3	$129.34	10.430%	$142.8302	$142.83	$142.85	$142.80
Purchase #4	$55.88	7.280%	$59.9481	$59.95	$59.95	$59.90
Purchase #5	$231.93	12.111%	$260.019	$260.02	$260.00	$260.00
Purchase #6	$103.93	7.462%	$111.6853	$111.69	$111.70	$111.70
Purchase #7	$129.38	5.310%	$136.2501	$136.25	$136.25	$136.30
7 purchase totals =	$903.12		$988.8045	$988.82	$988.85	$988.70