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	$233.46	10.712%	$258.4682	$258.47	$258.45	$258.50
Purchase #2	$120.93	3.319%	$124.9437	$124.94	$124.95	$124.90
Purchase #3	$175.52	13.526%	$199.2608	$199.26	$199.25	$199.30
Purchase #4	$248.76	11.352%	$276.9992	$277.00	$277.00	$277.00
Purchase #5	$97.40	12.830%	$109.8964	$109.90	$109.90	$109.90
Purchase #6	$73.81	9.106%	$80.5311	$80.53	$80.55	$80.50
Purchase #7	$150.57	13.799%	$171.3472	$171.35	$171.35	$171.30
7 purchase totals =	$1,100.45		$1,221.4466	$1,221.45	$1,221.45	$1,221.40