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	$99.49	13.600%	$113.0206	$113.02	$113.00	$113.00
Purchase #2	$243.32	11.185%	$270.5353	$270.54	$270.55	$270.50
Purchase #3	$98.56	13.665%	$112.0282	$112.03	$112.05	$112.00
Purchase #4	$24.84	13.144%	$28.105	$28.11	$28.10	$28.10
Purchase #5	$160.33	5.739%	$169.5313	$169.53	$169.55	$169.50
Purchase #6	$87.43	13.697%	$99.4053	$99.41	$99.40	$99.40
Purchase #7	$249.53	10.196%	$274.9721	$274.97	$274.95	$275.00
7 purchase totals =	$963.50		$1,067.5978	$1,067.61	$1,067.60	$1,067.50