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	$31.56	12.761%	$35.5874	$35.59	$35.60	$35.60
Purchase #2	$124.94	13.158%	$141.3796	$141.38	$141.40	$141.40
Purchase #3	$201.69	11.344%	$224.5697	$224.57	$224.55	$224.60
Purchase #4	$78.99	4.372%	$82.4434	$82.44	$82.45	$82.40
Purchase #5	$221.44	11.271%	$246.3985	$246.40	$246.40	$246.40
Purchase #6	$191.46	8.270%	$207.2937	$207.29	$207.30	$207.30
Purchase #7	$130.85	10.119%	$144.0907	$144.09	$144.10	$144.10
7 purchase totals =	$980.93		$1,081.7630	$1,081.76	$1,081.80	$1,081.80