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	$240.57	13.317%	$272.6067	$272.61	$272.60	$272.60
Purchase #2	$217.89	11.219%	$242.3351	$242.34	$242.35	$242.30
Purchase #3	$142.66	12.481%	$160.4654	$160.47	$160.45	$160.50
Purchase #4	$211.74	3.420%	$218.9815	$218.98	$219.00	$219.00
Purchase #5	$6.78	11.366%	$7.5506	$7.55	$7.55	$7.60
Purchase #6	$39.77	6.392%	$42.3121	$42.31	$42.30	$42.30
Purchase #7	$58.63	12.627%	$66.0332	$66.03	$66.05	$66.00
7 purchase totals =	$918.04		$1,010.2846	$1,010.29	$1,010.30	$1,010.30