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	$244.62	11.764%	$273.3971	$273.40	$273.40	$273.40
Purchase #2	$53.61	11.569%	$59.8121	$59.81	$59.80	$59.80
Purchase #3	$67.95	5.516%	$71.6981	$71.70	$71.70	$71.70
Purchase #4	$215.81	7.443%	$231.8727	$231.87	$231.85	$231.90
Purchase #5	$167.47	6.306%	$178.0307	$178.03	$178.05	$178.00
Purchase #6	$243.52	9.865%	$267.5432	$267.54	$267.55	$267.50
Purchase #7	$38.78	8.694%	$42.1515	$42.15	$42.15	$42.20
7 purchase totals =	$1,031.76		$1,124.5054	$1,124.50	$1,124.50	$1,124.50