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	$149.94	6.317%	$159.4117	$159.41	$159.40	$159.40
Purchase #2	$186.97	11.805%	$209.0418	$209.04	$209.05	$209.00
Purchase #3	$199.29	5.632%	$210.514	$210.51	$210.50	$210.50
Purchase #4	$126.31	3.233%	$130.3936	$130.39	$130.40	$130.40
Purchase #5	$115.95	13.274%	$131.3412	$131.34	$131.35	$131.30
Purchase #6	$52.66	9.270%	$57.5416	$57.54	$57.55	$57.50
Purchase #7	$98.33	6.631%	$104.8503	$104.85	$104.85	$104.90
7 purchase totals =	$929.45		$1,003.0942	$1,003.08	$1,003.10	$1,003.00