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	$56.25	6.275%	$59.7797	$59.78	$59.80	$59.80
Purchase #2	$63.30	8.805%	$68.8736	$68.87	$68.85	$68.90
Purchase #3	$195.85	11.391%	$218.1593	$218.16	$218.15	$218.20
Purchase #4	$168.32	12.835%	$189.9239	$189.92	$189.90	$189.90
Purchase #5	$116.44	13.164%	$131.7682	$131.77	$131.75	$131.80
Purchase #6	$128.95	10.741%	$142.8005	$142.80	$142.80	$142.80
Purchase #7	$151.25	9.744%	$165.9878	$165.99	$166.00	$166.00
7 purchase totals =	$880.36		$977.2930	$977.29	$977.25	$977.40