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	$188.97	12.310%	$212.2322	$212.23	$212.25	$212.20
Purchase #2	$68.96	9.504%	$75.514	$75.51	$75.50	$75.50
Purchase #3	$249.55	13.132%	$282.3209	$282.32	$282.30	$282.30
Purchase #4	$155.79	7.221%	$167.0396	$167.04	$167.05	$167.00
Purchase #5	$246.54	13.758%	$280.459	$280.46	$280.45	$280.50
Purchase #6	$77.33	7.209%	$82.9047	$82.90	$82.90	$82.90
Purchase #7	$146.89	9.170%	$160.3598	$160.36	$160.35	$160.40
7 purchase totals =	$1,134.03		$1,260.8302	$1,260.82	$1,260.80	$1,260.80