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	$106.37	13.388%	$120.6108	$120.61	$120.60	$120.60
Purchase #2	$119.74	3.515%	$123.9489	$123.95	$123.95	$123.90
Purchase #3	$39.79	7.798%	$42.8928	$42.89	$42.90	$42.90
Purchase #4	$212.57	3.148%	$219.2617	$219.26	$219.25	$219.30
Purchase #5	$207.49	12.718%	$233.8786	$233.88	$233.90	$233.90
Purchase #6	$137.59	9.815%	$151.0945	$151.09	$151.10	$151.10
Purchase #7	$36.70	8.642%	$39.8716	$39.87	$39.85	$39.90
7 purchase totals =	$860.25		$931.5589	$931.55	$931.55	$931.60