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	$204.53	10.737%	$226.4904	$226.49	$226.50	$226.50
Purchase #2	$180.78	11.800%	$202.112	$202.11	$202.10	$202.10
Purchase #3	$94.44	6.440%	$100.5219	$100.52	$100.50	$100.50
Purchase #4	$94.54	10.582%	$104.5442	$104.54	$104.55	$104.50
Purchase #5	$83.31	8.655%	$90.5205	$90.52	$90.50	$90.50
Purchase #6	$124.63	3.344%	$128.7976	$128.80	$128.80	$128.80
Purchase #7	$208.36	5.359%	$219.526	$219.53	$219.55	$219.50
7 purchase totals =	$990.59		$1,072.5126	$1,072.51	$1,072.50	$1,072.40