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	$22.77	11.185%	$25.3168	$25.32	$25.30	$25.30
Purchase #2	$244.31	10.530%	$270.0358	$270.04	$270.05	$270.00
Purchase #3	$63.72	7.491%	$68.4933	$68.49	$68.50	$68.50
Purchase #4	$152.46	11.193%	$169.5248	$169.52	$169.50	$169.50
Purchase #5	$193.53	12.807%	$218.3154	$218.32	$218.30	$218.30
Purchase #6	$140.48	7.314%	$150.7547	$150.75	$150.75	$150.80
Purchase #7	$198.35	5.285%	$208.8328	$208.83	$208.85	$208.80
7 purchase totals =	$1,015.62		$1,111.2736	$1,111.27	$1,111.25	$1,111.20