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	$114.99	7.246%	$123.3222	$123.32	$123.30	$123.30
Purchase #2	$162.72	5.648%	$171.9104	$171.91	$171.90	$171.90
Purchase #3	$112.38	3.704%	$116.5426	$116.54	$116.55	$116.50
Purchase #4	$84.48	5.613%	$89.2219	$89.22	$89.20	$89.20
Purchase #5	$148.86	12.386%	$167.2978	$167.30	$167.30	$167.30
Purchase #6	$12.38	9.563%	$13.5639	$13.56	$13.55	$13.60
Purchase #7	$144.97	3.747%	$150.402	$150.40	$150.40	$150.40
7 purchase totals =	$780.78		$832.2608	$832.25	$832.20	$832.20