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	$20.80	3.252%	$21.4764	$21.48	$21.50	$21.50
Purchase #2	$110.36	3.189%	$113.8794	$113.88	$113.90	$113.90
Purchase #3	$35.56	5.782%	$37.6161	$37.62	$37.60	$37.60
Purchase #4	$191.80	8.358%	$207.8306	$207.83	$207.85	$207.80
Purchase #5	$224.91	6.762%	$240.1184	$240.12	$240.10	$240.10
Purchase #6	$196.63	11.289%	$218.8276	$218.83	$218.85	$218.80
Purchase #7	$246.66	9.183%	$269.3108	$269.31	$269.30	$269.30
7 purchase totals =	$1,026.72		$1,109.0593	$1,109.07	$1,109.10	$1,109.00