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	$112.53	6.843%	$120.2304	$120.23	$120.25	$120.20
Purchase #2	$218.72	3.226%	$225.7759	$225.78	$225.80	$225.80
Purchase #3	$131.48	5.853%	$139.1755	$139.18	$139.20	$139.20
Purchase #4	$66.79	7.312%	$71.6737	$71.67	$71.65	$71.70
Purchase #5	$199.74	12.214%	$224.1362	$224.14	$224.15	$224.10
Purchase #6	$177.55	10.393%	$196.0028	$196.00	$196.00	$196.00
Purchase #7	$222.69	10.243%	$245.5001	$245.50	$245.50	$245.50
7 purchase totals =	$1,129.50		$1,222.4946	$1,222.50	$1,222.55	$1,222.50