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	$135.71	5.640%	$143.364	$143.36	$143.35	$143.40
Purchase #2	$85.59	4.422%	$89.3748	$89.37	$89.35	$89.40
Purchase #3	$156.66	9.660%	$171.7934	$171.79	$171.80	$171.80
Purchase #4	$218.37	11.541%	$243.5721	$243.57	$243.55	$243.60
Purchase #5	$135.37	7.122%	$145.0111	$145.01	$145.00	$145.00
Purchase #6	$151.69	8.332%	$164.3288	$164.33	$164.35	$164.30
Purchase #7	$186.39	6.847%	$199.1521	$199.15	$199.15	$199.20
7 purchase totals =	$1,069.78		$1,156.5963	$1,156.58	$1,156.55	$1,156.70