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	$171.47	6.197%	$182.096	$182.10	$182.10	$182.10
Purchase #2	$76.56	11.411%	$85.2963	$85.30	$85.30	$85.30
Purchase #3	$175.66	8.692%	$190.9284	$190.93	$190.95	$190.90
Purchase #4	$39.68	4.713%	$41.5501	$41.55	$41.55	$41.60
Purchase #5	$12.32	6.562%	$13.1284	$13.13	$13.15	$13.10
Purchase #6	$78.54	4.794%	$82.3052	$82.31	$82.30	$82.30
Purchase #7	$67.32	7.286%	$72.2249	$72.22	$72.20	$72.20
7 purchase totals =	$621.55		$667.5293	$667.54	$667.55	$667.50