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	$106.83	12.346%	$120.0192	$120.02	$120.00	$120.00
Purchase #2	$169.90	10.864%	$188.3579	$188.36	$188.35	$188.40
Purchase #3	$216.65	12.401%	$243.5168	$243.52	$243.50	$243.50
Purchase #4	$108.81	3.686%	$112.8207	$112.82	$112.80	$112.80
Purchase #5	$216.81	7.702%	$233.5087	$233.51	$233.50	$233.50
Purchase #6	$187.85	4.795%	$196.8574	$196.86	$196.85	$196.90
Purchase #7	$218.95	12.736%	$246.8355	$246.84	$246.85	$246.80
7 purchase totals =	$1,225.80		$1,341.9162	$1,341.93	$1,341.85	$1,341.90