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	$228.67	4.827%	$239.7079	$239.71	$239.70	$239.70
Purchase #2	$33.90	4.595%	$35.4577	$35.46	$35.45	$35.50
Purchase #3	$83.36	7.266%	$89.4169	$89.42	$89.40	$89.40
Purchase #4	$76.68	4.596%	$80.2042	$80.20	$80.20	$80.20
Purchase #5	$229.96	4.446%	$240.184	$240.18	$240.20	$240.20
Purchase #6	$179.49	9.570%	$196.6672	$196.67	$196.65	$196.70
Purchase #7	$108.88	11.848%	$121.7801	$121.78	$121.80	$121.80
7 purchase totals =	$940.94		$1,003.4180	$1,003.42	$1,003.40	$1,003.50