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	$72.90	12.223%	$81.8106	$81.81	$81.80	$81.80
Purchase #2	$213.48	4.185%	$222.4141	$222.41	$222.40	$222.40
Purchase #3	$246.92	7.301%	$264.9476	$264.95	$264.95	$264.90
Purchase #4	$35.62	7.283%	$38.2142	$38.21	$38.20	$38.20
Purchase #5	$117.28	13.726%	$133.3779	$133.38	$133.40	$133.40
Purchase #6	$140.42	8.442%	$152.2743	$152.27	$152.25	$152.30
Purchase #7	$91.44	3.740%	$94.8599	$94.86	$94.85	$94.90
7 purchase totals =	$918.06		$987.8986	$987.89	$987.85	$987.90