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	$165.63	13.661%	$188.2567	$188.26	$188.25	$188.30
Purchase #2	$75.50	4.392%	$78.816	$78.82	$78.80	$78.80
Purchase #3	$171.41	9.643%	$187.9391	$187.94	$187.95	$187.90
Purchase #4	$81.55	4.448%	$85.1773	$85.18	$85.20	$85.20
Purchase #5	$53.41	10.285%	$58.9032	$58.90	$58.90	$58.90
Purchase #6	$194.87	12.334%	$218.9053	$218.91	$218.90	$218.90
Purchase #7	$146.67	10.370%	$161.8797	$161.88	$161.90	$161.90
7 purchase totals =	$889.04		$979.8773	$979.89	$979.90	$979.90