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	$85.67	12.740%	$96.5844	$96.58	$96.60	$96.60
Purchase #2	$179.90	12.767%	$202.8678	$202.87	$202.85	$202.90
Purchase #3	$66.71	4.118%	$69.4571	$69.46	$69.45	$69.50
Purchase #4	$139.50	12.212%	$156.5357	$156.54	$156.55	$156.50
Purchase #5	$32.72	11.652%	$36.5325	$36.53	$36.55	$36.50
Purchase #6	$228.67	8.696%	$248.5551	$248.56	$248.55	$248.60
Purchase #7	$150.49	11.659%	$168.0356	$168.04	$168.05	$168.00
7 purchase totals =	$883.66		$978.5682	$978.58	$978.60	$978.60