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	$172.90	9.821%	$189.8805	$189.88	$189.90	$189.90
Purchase #2	$43.79	10.214%	$48.2627	$48.26	$48.25	$48.30
Purchase #3	$60.33	13.368%	$68.3949	$68.39	$68.40	$68.40
Purchase #4	$59.95	11.619%	$66.9156	$66.92	$66.90	$66.90
Purchase #5	$193.91	11.132%	$215.4961	$215.50	$215.50	$215.50
Purchase #6	$58.43	7.471%	$62.7953	$62.80	$62.80	$62.80
Purchase #7	$68.84	4.280%	$71.7864	$71.79	$71.80	$71.80
7 purchase totals =	$658.15		$723.5315	$723.54	$723.55	$723.60