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	$33.80	10.825%	$37.4589	$37.46	$37.45	$37.50
Purchase #2	$85.43	10.555%	$94.4471	$94.45	$94.45	$94.40
Purchase #3	$202.97	12.752%	$228.8527	$228.85	$228.85	$228.90
Purchase #4	$161.50	11.365%	$179.8545	$179.85	$179.85	$179.90
Purchase #5	$11.79	12.210%	$13.2296	$13.23	$13.25	$13.20
Purchase #6	$25.68	11.103%	$28.5313	$28.53	$28.55	$28.50
Purchase #7	$38.45	10.228%	$42.3827	$42.38	$42.40	$42.40
7 purchase totals =	$559.62		$624.7568	$624.75	$624.80	$624.80