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	$35.79	10.668%	$39.6081	$39.61	$39.60	$39.60
Purchase #2	$182.95	7.195%	$196.1133	$196.11	$196.10	$196.10
Purchase #3	$83.35	9.811%	$91.5275	$91.53	$91.55	$91.50
Purchase #4	$112.46	6.343%	$119.5933	$119.59	$119.60	$119.60
Purchase #5	$82.76	9.110%	$90.2994	$90.30	$90.30	$90.30
Purchase #6	$242.76	12.823%	$273.8891	$273.89	$273.90	$273.90
Purchase #7	$128.33	4.256%	$133.7917	$133.79	$133.80	$133.80
7 purchase totals =	$868.40		$944.8224	$944.82	$944.85	$944.80