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	$183.60	12.595%	$206.7244	$206.72	$206.70	$206.70
Purchase #2	$35.25	6.338%	$37.4841	$37.48	$37.50	$37.50
Purchase #3	$87.50	6.107%	$92.8436	$92.84	$92.85	$92.80
Purchase #4	$91.50	11.209%	$101.7562	$101.76	$101.75	$101.80
Purchase #5	$123.57	6.731%	$131.8875	$131.89	$131.90	$131.90
Purchase #6	$137.44	5.800%	$145.4115	$145.41	$145.40	$145.40
Purchase #7	$150.58	3.436%	$155.7539	$155.75	$155.75	$155.80
7 purchase totals =	$809.44		$871.8612	$871.85	$871.85	$871.90