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	$180.69	4.709%	$189.1987	$189.20	$189.20	$189.20
Purchase #2	$168.68	9.374%	$184.4921	$184.49	$184.50	$184.50
Purchase #3	$201.39	3.510%	$208.4588	$208.46	$208.45	$208.50
Purchase #4	$81.60	5.767%	$86.3059	$86.31	$86.30	$86.30
Purchase #5	$81.90	9.745%	$89.8812	$89.88	$89.90	$89.90
Purchase #6	$124.35	13.473%	$141.1037	$141.10	$141.10	$141.10
Purchase #7	$106.38	13.301%	$120.5296	$120.53	$120.55	$120.50
7 purchase totals =	$944.99		$1,019.9700	$1,019.97	$1,020.00	$1,020.00