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	$65.44	6.445%	$69.6576	$69.66	$69.65	$69.70
Purchase #2	$50.89	9.402%	$55.6747	$55.67	$55.65	$55.70
Purchase #3	$212.90	13.249%	$241.1071	$241.11	$241.10	$241.10
Purchase #4	$111.48	5.421%	$117.5233	$117.52	$117.50	$117.50
Purchase #5	$105.55	6.569%	$112.4836	$112.48	$112.50	$112.50
Purchase #6	$82.89	11.781%	$92.6553	$92.66	$92.65	$92.70
Purchase #7	$155.85	5.405%	$164.2737	$164.27	$164.25	$164.30
7 purchase totals =	$785.00		$853.3753	$853.37	$853.30	$853.50