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	$198.25	12.190%	$222.4167	$222.42	$222.40	$222.40
Purchase #2	$90.48	4.472%	$94.5263	$94.53	$94.55	$94.50
Purchase #3	$63.97	7.637%	$68.8554	$68.86	$68.85	$68.90
Purchase #4	$36.25	3.445%	$37.4988	$37.50	$37.50	$37.50
Purchase #5	$199.42	11.196%	$221.7471	$221.75	$221.75	$221.70
Purchase #6	$196.63	8.339%	$213.027	$213.03	$213.05	$213.00
Purchase #7	$42.58	6.313%	$45.2681	$45.27	$45.25	$45.30
7 purchase totals =	$827.58		$903.3394	$903.36	$903.35	$903.30