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	$74.72	12.402%	$83.9868	$83.99	$84.00	$84.00
Purchase #2	$166.51	7.658%	$179.2613	$179.26	$179.25	$179.30
Purchase #3	$218.85	6.410%	$232.8783	$232.88	$232.90	$232.90
Purchase #4	$232.29	12.785%	$261.9883	$261.99	$262.00	$262.00
Purchase #5	$102.27	8.868%	$111.3393	$111.34	$111.35	$111.30
Purchase #6	$160.45	12.442%	$180.4132	$180.41	$180.40	$180.40
Purchase #7	$131.48	11.525%	$146.6331	$146.63	$146.65	$146.60
7 purchase totals =	$1,086.57		$1,196.5003	$1,196.50	$1,196.55	$1,196.50