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	$245.72	11.652%	$274.3513	$274.35	$274.35	$274.40
Purchase #2	$204.47	7.349%	$219.4965	$219.50	$219.50	$219.50
Purchase #3	$135.59	11.742%	$151.511	$151.51	$151.50	$151.50
Purchase #4	$37.93	10.738%	$42.0029	$42.00	$42.00	$42.00
Purchase #5	$246.94	13.764%	$280.9288	$280.93	$280.95	$280.90
Purchase #6	$77.90	3.742%	$80.815	$80.82	$80.80	$80.80
Purchase #7	$182.33	12.290%	$204.7384	$204.74	$204.75	$204.70
7 purchase totals =	$1,130.88		$1,253.8439	$1,253.85	$1,253.85	$1,253.80