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	$6.99	4.275%	$7.2888	$7.29	$7.30	$7.30
Purchase #2	$203.95	11.666%	$227.7428	$227.74	$227.75	$227.70
Purchase #3	$227.79	6.270%	$242.0724	$242.07	$242.05	$242.10
Purchase #4	$90.60	5.543%	$95.622	$95.62	$95.60	$95.60
Purchase #5	$77.86	9.708%	$85.4186	$85.42	$85.40	$85.40
Purchase #6	$210.58	10.134%	$231.9202	$231.92	$231.90	$231.90
Purchase #7	$162.31	3.188%	$167.4844	$167.48	$167.50	$167.50
7 purchase totals =	$980.08		$1,057.5492	$1,057.54	$1,057.50	$1,057.50