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	$248.76	8.729%	$270.4743	$270.47	$270.45	$270.50
Purchase #2	$92.27	6.404%	$98.179	$98.18	$98.20	$98.20
Purchase #3	$185.97	5.422%	$196.0533	$196.05	$196.05	$196.10
Purchase #4	$77.61	3.388%	$80.2394	$80.24	$80.25	$80.20
Purchase #5	$42.43	8.240%	$45.9262	$45.93	$45.95	$45.90
Purchase #6	$234.97	3.548%	$243.3067	$243.31	$243.30	$243.30
Purchase #7	$185.25	3.553%	$191.8319	$191.83	$191.85	$191.80
7 purchase totals =	$1,067.26		$1,126.0108	$1,126.01	$1,126.05	$1,126.00