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	$245.85	10.874%	$272.5837	$272.58	$272.60	$272.60
Purchase #2	$85.69	7.202%	$91.8614	$91.86	$91.85	$91.90
Purchase #3	$65.36	11.305%	$72.7489	$72.75	$72.75	$72.70
Purchase #4	$52.65	5.493%	$55.5421	$55.54	$55.55	$55.50
Purchase #5	$109.98	12.759%	$124.0123	$124.01	$124.00	$124.00
Purchase #6	$69.82	11.503%	$77.8514	$77.85	$77.85	$77.90
Purchase #7	$245.29	8.406%	$265.9091	$265.91	$265.90	$265.90
7 purchase totals =	$874.64		$960.5089	$960.50	$960.50	$960.50