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	$182.82	4.237%	$190.5661	$190.57	$190.55	$190.60
Purchase #2	$90.48	9.325%	$98.9173	$98.92	$98.90	$98.90
Purchase #3	$192.78	13.537%	$218.8766	$218.88	$218.90	$218.90
Purchase #4	$73.53	7.570%	$79.0962	$79.10	$79.10	$79.10
Purchase #5	$35.85	13.430%	$40.6647	$40.66	$40.65	$40.70
Purchase #6	$179.26	10.640%	$198.3333	$198.33	$198.35	$198.30
Purchase #7	$101.83	11.712%	$113.7563	$113.76	$113.75	$113.80
7 purchase totals =	$856.55		$940.2105	$940.22	$940.20	$940.30