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	$141.87	3.543%	$146.8965	$146.90	$146.90	$146.90
Purchase #2	$69.53	4.833%	$72.8904	$72.89	$72.90	$72.90
Purchase #3	$170.53	10.223%	$187.9633	$187.96	$187.95	$188.00
Purchase #4	$64.38	4.839%	$67.4953	$67.50	$67.50	$67.50
Purchase #5	$151.38	8.555%	$164.3306	$164.33	$164.35	$164.30
Purchase #6	$8.99	13.783%	$10.2291	$10.23	$10.25	$10.20
Purchase #7	$180.74	6.482%	$192.4556	$192.46	$192.45	$192.50
7 purchase totals =	$787.42		$842.2608	$842.27	$842.30	$842.30