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	$19.97	4.642%	$20.897	$20.90	$20.90	$20.90
Purchase #2	$106.32	12.821%	$119.9513	$119.95	$119.95	$120.00
Purchase #3	$28.73	11.264%	$31.9661	$31.97	$31.95	$32.00
Purchase #4	$82.61	9.815%	$90.7182	$90.72	$90.70	$90.70
Purchase #5	$166.93	7.711%	$179.802	$179.80	$179.80	$179.80
Purchase #6	$83.69	4.796%	$87.7038	$87.70	$87.70	$87.70
Purchase #7	$6.52	13.732%	$7.4153	$7.42	$7.40	$7.40
7 purchase totals =	$494.77		$538.4537	$538.46	$538.40	$538.50