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	$104.94	12.710%	$118.2779	$118.28	$118.30	$118.30
Purchase #2	$21.67	8.111%	$23.4277	$23.43	$23.45	$23.40
Purchase #3	$243.72	3.299%	$251.7603	$251.76	$251.75	$251.80
Purchase #4	$174.33	7.595%	$187.5704	$187.57	$187.55	$187.60
Purchase #5	$148.34	8.455%	$160.8821	$160.88	$160.90	$160.90
Purchase #6	$188.62	11.413%	$210.1472	$210.15	$210.15	$210.10
Purchase #7	$52.82	12.459%	$59.4008	$59.40	$59.40	$59.40
7 purchase totals =	$934.44		$1,011.4664	$1,011.47	$1,011.50	$1,011.50