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	$172.92	9.648%	$189.6033	$189.60	$189.60	$189.60
Purchase #2	$78.99	3.779%	$81.975	$81.98	$82.00	$82.00
Purchase #3	$97.37	12.517%	$109.5578	$109.56	$109.55	$109.60
Purchase #4	$28.83	11.507%	$32.1475	$32.15	$32.15	$32.10
Purchase #5	$37.41	13.338%	$42.3997	$42.40	$42.40	$42.40
Purchase #6	$219.52	4.170%	$228.674	$228.67	$228.65	$228.70
Purchase #7	$135.88	11.520%	$151.5334	$151.53	$151.55	$151.50
7 purchase totals =	$770.92		$835.8907	$835.89	$835.90	$835.90