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	$116.31	6.718%	$124.1237	$124.12	$124.10	$124.10
Purchase #2	$80.86	13.137%	$91.4826	$91.48	$91.50	$91.50
Purchase #3	$247.88	10.366%	$273.5752	$273.58	$273.60	$273.60
Purchase #4	$119.89	12.274%	$134.6053	$134.61	$134.60	$134.60
Purchase #5	$221.85	12.223%	$248.9667	$248.97	$248.95	$249.00
Purchase #6	$33.94	4.862%	$35.5902	$35.59	$35.60	$35.60
Purchase #7	$182.89	7.398%	$196.4202	$196.42	$196.40	$196.40
7 purchase totals =	$1,003.62		$1,104.7639	$1,104.77	$1,104.75	$1,104.80