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	$87.71	13.477%	$99.5307	$99.53	$99.55	$99.50
Purchase #2	$111.59	10.712%	$123.5435	$123.54	$123.55	$123.50
Purchase #3	$37.63	11.636%	$42.0086	$42.01	$42.00	$42.00
Purchase #4	$52.49	8.206%	$56.7973	$56.80	$56.80	$56.80
Purchase #5	$249.33	10.689%	$275.9809	$275.98	$276.00	$276.00
Purchase #6	$136.71	13.610%	$155.3162	$155.32	$155.30	$155.30
Purchase #7	$194.53	9.819%	$213.6309	$213.63	$213.65	$213.60
7 purchase totals =	$869.99		$966.8081	$966.81	$966.85	$966.70