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	$150.94	13.695%	$171.6112	$171.61	$171.60	$171.60
Purchase #2	$81.95	9.267%	$89.5443	$89.54	$89.55	$89.50
Purchase #3	$31.68	5.582%	$33.4484	$33.45	$33.45	$33.40
Purchase #4	$80.70	7.678%	$86.8961	$86.90	$86.90	$86.90
Purchase #5	$212.88	12.306%	$239.077	$239.08	$239.10	$239.10
Purchase #6	$131.53	5.322%	$138.53	$138.53	$138.55	$138.50
Purchase #7	$89.42	11.354%	$99.5727	$99.57	$99.55	$99.60
7 purchase totals =	$779.10		$858.6797	$858.68	$858.70	$858.60