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	$44.65	5.853%	$47.2634	$47.26	$47.25	$47.30
Purchase #2	$146.39	10.278%	$161.436	$161.44	$161.45	$161.40
Purchase #3	$168.50	11.577%	$188.0072	$188.01	$188.00	$188.00
Purchase #4	$131.86	9.573%	$144.483	$144.48	$144.50	$144.50
Purchase #5	$227.37	9.771%	$249.5863	$249.59	$249.60	$249.60
Purchase #6	$85.46	4.486%	$89.2937	$89.29	$89.30	$89.30
Purchase #7	$45.44	4.392%	$47.4357	$47.44	$47.45	$47.40
7 purchase totals =	$849.67		$927.5053	$927.51	$927.55	$927.50