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	$53.45	13.169%	$60.4888	$60.49	$60.50	$60.50
Purchase #2	$250.35	9.687%	$274.6014	$274.60	$274.60	$274.60
Purchase #3	$180.39	11.611%	$201.3351	$201.34	$201.35	$201.30
Purchase #4	$81.66	9.513%	$89.4283	$89.43	$89.45	$89.40
Purchase #5	$96.87	7.120%	$103.7671	$103.77	$103.75	$103.80
Purchase #6	$180.39	3.611%	$186.9039	$186.90	$186.90	$186.90
Purchase #7	$168.27	12.512%	$189.3239	$189.32	$189.30	$189.30
7 purchase totals =	$1,011.38		$1,105.8485	$1,105.85	$1,105.85	$1,105.80