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	$124.40	3.588%	$128.8635	$128.86	$128.85	$128.90
Purchase #2	$188.44	6.364%	$200.4323	$200.43	$200.45	$200.40
Purchase #3	$12.36	9.253%	$13.5037	$13.50	$13.50	$13.50
Purchase #4	$115.39	3.312%	$119.2117	$119.21	$119.20	$119.20
Purchase #5	$96.79	7.604%	$104.1499	$104.15	$104.15	$104.10
Purchase #6	$154.65	6.515%	$164.7254	$164.73	$164.75	$164.70
Purchase #7	$116.55	12.498%	$131.1164	$131.12	$131.10	$131.10
7 purchase totals =	$808.58		$862.0029	$862.00	$862.00	$861.90