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	$131.43	7.112%	$140.7773	$140.78	$140.80	$140.80
Purchase #2	$55.58	7.819%	$59.9258	$59.93	$59.95	$59.90
Purchase #3	$130.30	3.137%	$134.3875	$134.39	$134.40	$134.40
Purchase #4	$83.85	7.832%	$90.4171	$90.42	$90.40	$90.40
Purchase #5	$178.36	6.843%	$190.5652	$190.57	$190.55	$190.60
Purchase #6	$73.55	10.641%	$81.3765	$81.38	$81.40	$81.40
Purchase #7	$153.39	13.507%	$174.1084	$174.11	$174.10	$174.10
7 purchase totals =	$806.46		$871.5578	$871.58	$871.60	$871.60