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	$84.89	10.158%	$93.5131	$93.51	$93.50	$93.50
Purchase #2	$241.44	11.610%	$269.4712	$269.47	$269.45	$269.50
Purchase #3	$96.80	8.864%	$105.3804	$105.38	$105.40	$105.40
Purchase #4	$18.62	11.390%	$20.7408	$20.74	$20.75	$20.70
Purchase #5	$120.61	7.465%	$129.6135	$129.61	$129.60	$129.60
Purchase #6	$41.45	3.380%	$42.851	$42.85	$42.85	$42.90
Purchase #7	$5.33	3.576%	$5.5206	$5.52	$5.50	$5.50
7 purchase totals =	$609.14		$667.0906	$667.08	$667.05	$667.10