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	$197.47	4.764%	$206.8775	$206.88	$206.90	$206.90
Purchase #2	$228.75	11.833%	$255.818	$255.82	$255.80	$255.80
Purchase #3	$196.94	12.230%	$221.0258	$221.03	$221.05	$221.00
Purchase #4	$89.50	3.665%	$92.7802	$92.78	$92.80	$92.80
Purchase #5	$106.76	11.588%	$119.1313	$119.13	$119.15	$119.10
Purchase #6	$232.41	13.568%	$263.9434	$263.94	$263.95	$263.90
Purchase #7	$154.47	4.150%	$160.8805	$160.88	$160.90	$160.90
7 purchase totals =	$1,206.30		$1,320.4567	$1,320.46	$1,320.55	$1,320.40