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	$70.93	6.387%	$75.4603	$75.46	$75.45	$75.50
Purchase #2	$79.88	4.619%	$83.5697	$83.57	$83.55	$83.60
Purchase #3	$70.85	10.342%	$78.1773	$78.18	$78.20	$78.20
Purchase #4	$224.30	9.424%	$245.438	$245.44	$245.45	$245.40
Purchase #5	$86.61	4.472%	$90.4832	$90.48	$90.50	$90.50
Purchase #6	$7.60	11.535%	$8.4767	$8.48	$8.50	$8.50
Purchase #7	$176.56	7.512%	$189.8232	$189.82	$189.80	$189.80
7 purchase totals =	$716.73		$771.4284	$771.43	$771.45	$771.50