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	$72.53	11.736%	$81.0421	$81.04	$81.05	$81.00
Purchase #2	$53.39	7.156%	$57.2106	$57.21	$57.20	$57.20
Purchase #3	$247.28	11.760%	$276.3601	$276.36	$276.35	$276.40
Purchase #4	$231.81	10.694%	$256.5998	$256.60	$256.60	$256.60
Purchase #5	$250.66	6.870%	$267.8803	$267.88	$267.90	$267.90
Purchase #6	$94.66	11.513%	$105.5582	$105.56	$105.55	$105.60
Purchase #7	$92.93	8.121%	$100.4768	$100.48	$100.50	$100.50
7 purchase totals =	$1,043.26		$1,145.1279	$1,145.13	$1,145.15	$1,145.20