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	$172.35	7.692%	$185.6072	$185.61	$185.60	$185.60
Purchase #2	$83.53	9.867%	$91.7719	$91.77	$91.75	$91.80
Purchase #3	$63.94	13.571%	$72.6173	$72.62	$72.60	$72.60
Purchase #4	$41.76	12.290%	$46.8923	$46.89	$46.90	$46.90
Purchase #5	$156.93	8.852%	$170.8214	$170.82	$170.80	$170.80
Purchase #6	$212.80	12.588%	$239.5873	$239.59	$239.60	$239.60
Purchase #7	$249.43	12.478%	$280.5539	$280.55	$280.55	$280.60
7 purchase totals =	$980.74		$1,087.8513	$1,087.85	$1,087.80	$1,087.90