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	$79.81	3.277%	$82.4254	$82.43	$82.45	$82.40
Purchase #2	$62.98	5.450%	$66.4124	$66.41	$66.40	$66.40
Purchase #3	$112.95	9.664%	$123.8655	$123.87	$123.85	$123.90
Purchase #4	$203.89	11.511%	$227.3598	$227.36	$227.35	$227.40
Purchase #5	$102.98	6.790%	$109.9723	$109.97	$109.95	$110.00
Purchase #6	$94.34	7.387%	$101.3089	$101.31	$101.30	$101.30
Purchase #7	$83.97	10.661%	$92.922	$92.92	$92.90	$92.90
7 purchase totals =	$740.92		$804.2663	$804.27	$804.20	$804.30