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	$189.99	4.459%	$198.4617	$198.46	$198.45	$198.50
Purchase #2	$48.93	8.698%	$53.1859	$53.19	$53.20	$53.20
Purchase #3	$234.48	12.233%	$263.1639	$263.16	$263.15	$263.20
Purchase #4	$78.90	8.215%	$85.3816	$85.38	$85.40	$85.40
Purchase #5	$119.72	10.171%	$131.8967	$131.90	$131.90	$131.90
Purchase #6	$137.82	13.517%	$156.4491	$156.45	$156.45	$156.40
Purchase #7	$220.65	6.789%	$235.6299	$235.63	$235.65	$235.60
7 purchase totals =	$1,030.49		$1,124.1688	$1,124.17	$1,124.20	$1,124.20