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	$186.34	7.511%	$200.336	$200.34	$200.35	$200.30
Purchase #2	$138.29	9.797%	$151.8383	$151.84	$151.85	$151.80
Purchase #3	$249.44	12.300%	$280.1211	$280.12	$280.10	$280.10
Purchase #4	$39.69	13.256%	$44.9513	$44.95	$44.95	$45.00
Purchase #5	$41.53	12.788%	$46.8409	$46.84	$46.85	$46.80
Purchase #6	$76.68	5.530%	$80.9204	$80.92	$80.90	$80.90
Purchase #7	$77.36	10.662%	$85.6081	$85.61	$85.60	$85.60
7 purchase totals =	$809.33		$890.6161	$890.62	$890.60	$890.50