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	$83.91	12.628%	$94.5062	$94.51	$94.50	$94.50
Purchase #2	$114.25	10.800%	$126.589	$126.59	$126.60	$126.60
Purchase #3	$53.46	11.646%	$59.686	$59.69	$59.70	$59.70
Purchase #4	$175.46	7.482%	$188.5879	$188.59	$188.60	$188.60
Purchase #5	$218.64	13.851%	$248.9238	$248.92	$248.90	$248.90
Purchase #6	$54.35	7.856%	$58.6197	$58.62	$58.60	$58.60
Purchase #7	$71.25	12.301%	$80.0145	$80.01	$80.00	$80.00
7 purchase totals =	$771.32		$856.9271	$856.93	$856.90	$856.90