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	$97.33	7.371%	$104.5042	$104.50	$104.50	$104.50
Purchase #2	$83.59	4.188%	$87.0907	$87.09	$87.10	$87.10
Purchase #3	$184.57	13.401%	$209.3042	$209.30	$209.30	$209.30
Purchase #4	$134.54	4.495%	$140.5876	$140.59	$140.60	$140.60
Purchase #5	$246.88	11.852%	$276.1402	$276.14	$276.15	$276.10
Purchase #6	$167.34	7.539%	$179.9558	$179.96	$179.95	$180.00
Purchase #7	$56.98	5.132%	$59.9042	$59.90	$59.90	$59.90
7 purchase totals =	$971.23		$1,057.4869	$1,057.48	$1,057.50	$1,057.50