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	$166.33	7.742%	$179.2073	$179.21	$179.20	$179.20
Purchase #2	$32.55	8.762%	$35.402	$35.40	$35.40	$35.40
Purchase #3	$184.33	13.658%	$209.5058	$209.51	$209.50	$209.50
Purchase #4	$168.40	6.223%	$178.8795	$178.88	$178.90	$178.90
Purchase #5	$38.72	9.225%	$42.2919	$42.29	$42.30	$42.30
Purchase #6	$41.45	5.518%	$43.7372	$43.74	$43.75	$43.70
Purchase #7	$174.85	13.659%	$198.7328	$198.73	$198.75	$198.70
7 purchase totals =	$806.63		$887.7565	$887.76	$887.80	$887.70