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	$39.93	6.274%	$42.4352	$42.44	$42.45	$42.40
Purchase #2	$23.97	7.701%	$25.8159	$25.82	$25.80	$25.80
Purchase #3	$120.64	13.275%	$136.655	$136.66	$136.65	$136.70
Purchase #4	$232.93	3.171%	$240.3162	$240.32	$240.30	$240.30
Purchase #5	$141.71	6.387%	$150.761	$150.76	$150.75	$150.80
Purchase #6	$36.91	13.831%	$42.015	$42.02	$42.00	$42.00
Purchase #7	$162.65	6.237%	$172.7945	$172.79	$172.80	$172.80
7 purchase totals =	$758.74		$810.7928	$810.81	$810.75	$810.80