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	$61.74	13.861%	$70.2978	$70.30	$70.30	$70.30
Purchase #2	$227.51	13.105%	$257.3252	$257.33	$257.35	$257.30
Purchase #3	$95.27	3.127%	$98.2491	$98.25	$98.25	$98.20
Purchase #4	$35.59	13.515%	$40.4	$40.40	$40.40	$40.40
Purchase #5	$57.47	6.833%	$61.3969	$61.40	$61.40	$61.40
Purchase #6	$232.55	3.328%	$240.2893	$240.29	$240.30	$240.30
Purchase #7	$219.97	9.679%	$241.2609	$241.26	$241.25	$241.30
7 purchase totals =	$930.10		$1,009.2192	$1,009.23	$1,009.25	$1,009.20