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	$111.25	4.109%	$115.8213	$115.82	$115.80	$115.80
Purchase #2	$87.72	3.521%	$90.8086	$90.81	$90.80	$90.80
Purchase #3	$225.75	6.533%	$240.4982	$240.50	$240.50	$240.50
Purchase #4	$18.75	11.804%	$20.9633	$20.96	$20.95	$21.00
Purchase #5	$142.89	6.644%	$152.3836	$152.38	$152.40	$152.40
Purchase #6	$189.94	12.314%	$213.3292	$213.33	$213.35	$213.30
Purchase #7	$5.53	7.813%	$5.9621	$5.96	$5.95	$6.00
7 purchase totals =	$781.83		$839.7663	$839.76	$839.75	$839.80