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	$90.34	12.488%	$101.6217	$101.62	$101.60	$101.60
Purchase #2	$13.64	13.373%	$15.4641	$15.46	$15.45	$15.50
Purchase #3	$200.45	9.258%	$219.0077	$219.01	$219.00	$219.00
Purchase #4	$29.79	7.261%	$31.9531	$31.95	$31.95	$32.00
Purchase #5	$219.36	9.539%	$240.2848	$240.28	$240.30	$240.30
Purchase #6	$61.80	8.371%	$66.9733	$66.97	$66.95	$67.00
Purchase #7	$81.92	4.498%	$85.6048	$85.60	$85.60	$85.60
7 purchase totals =	$697.30		$760.9095	$760.89	$760.85	$761.00