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	$52.38	6.406%	$55.7355	$55.74	$55.75	$55.70
Purchase #2	$220.76	8.348%	$239.189	$239.19	$239.20	$239.20
Purchase #3	$177.81	10.422%	$196.3414	$196.34	$196.35	$196.30
Purchase #4	$133.39	13.143%	$150.9214	$150.92	$150.90	$150.90
Purchase #5	$212.53	3.874%	$220.7634	$220.76	$220.75	$220.80
Purchase #6	$39.54	6.648%	$42.1686	$42.17	$42.15	$42.20
Purchase #7	$63.36	7.153%	$67.8921	$67.89	$67.90	$67.90
7 purchase totals =	$899.77		$973.0114	$973.01	$973.00	$973.00