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	$99.71	11.683%	$111.3591	$111.36	$111.35	$111.40
Purchase #2	$245.42	9.342%	$268.3471	$268.35	$268.35	$268.30
Purchase #3	$186.66	10.745%	$206.7166	$206.72	$206.70	$206.70
Purchase #4	$72.93	12.821%	$82.2804	$82.28	$82.30	$82.30
Purchase #5	$238.78	12.736%	$269.191	$269.19	$269.20	$269.20
Purchase #6	$202.55	10.715%	$224.2532	$224.25	$224.25	$224.30
Purchase #7	$17.97	13.526%	$20.4006	$20.40	$20.40	$20.40
7 purchase totals =	$1,064.02		$1,182.5480	$1,182.55	$1,182.55	$1,182.60