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	$134.31	12.628%	$151.2707	$151.27	$151.25	$151.30
Purchase #2	$217.34	6.443%	$231.3432	$231.34	$231.35	$231.30
Purchase #3	$96.94	9.539%	$106.1871	$106.19	$106.20	$106.20
Purchase #4	$50.55	12.602%	$56.9203	$56.92	$56.90	$56.90
Purchase #5	$53.33	4.669%	$55.82	$55.82	$55.80	$55.80
Purchase #6	$171.45	10.777%	$189.9272	$189.93	$189.95	$189.90
Purchase #7	$103.92	5.217%	$109.3415	$109.34	$109.35	$109.30
7 purchase totals =	$827.84		$900.8100	$900.81	$900.80	$900.70