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	$16.81	6.528%	$17.9074	$17.91	$17.90	$17.90
Purchase #2	$152.28	10.658%	$168.51	$168.51	$168.50	$168.50
Purchase #3	$192.44	10.595%	$212.829	$212.83	$212.85	$212.80
Purchase #4	$90.90	4.279%	$94.7896	$94.79	$94.80	$94.80
Purchase #5	$89.74	6.803%	$95.845	$95.85	$95.85	$95.80
Purchase #6	$171.54	6.483%	$182.6609	$182.66	$182.65	$182.70
Purchase #7	$29.81	7.209%	$31.959	$31.96	$31.95	$32.00
7 purchase totals =	$743.52		$804.5009	$804.51	$804.50	$804.50